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GeneralIs serpentine jade?
26th Apr 2013 13:10 UTCBill Cordua 🌟 Manager
26th Apr 2013 13:35 UTCChester S. Lemanski, Jr.
26th Apr 2013 14:02 UTCJolyon Ralph Founder
This part is true, all these minerals provide exactly the same metaphysical benefits.
Jolyon
26th Apr 2013 14:43 UTCDavid Von Bargen Manager
The FTC only regards nephrite and jadeite as jade. Jade is a gemological term, so you have to realize that you are dealing with people who stretch definitions quite a bit (who would assume that smoky topaz is actually quartz?)
http://www.geo.utexas.edu/courses/347k/redesign/gem_notes/jade/jade_main.htm
http://euromin.w3sites.net/Nouveau_site/histoire/antiqueMA/HISANTe.htm#9
26th Apr 2013 15:39 UTCKelly Nash 🌟 Expert
26th Apr 2013 17:18 UTCOwen Lewis
-------------------------------------------------------
> A lot of this problem goes back to the ancient
> (pre mineralogy development) cultures in Asia.
Primarily, it is the Chinese and not the Western nations who set the market in Jade. It is simple cultural arrogance (and very misplaced IMO) to presume that Western standards of arbitration shall apply elsewhere and, specifically in the the matter of the Chinese market, to what may or may not be properly sold as jade. In any event, globally the guidelines for jade and trading in it are presently in a state of flux, with reformation likely to be complete in 2014. There is already an international laboratory testing harmonisation agreement in respect to the admission of omphacite and kosmochor.
> When you classify things by color, everything
> greenish becomes jade.
Strange that you think so, David. Which dealers can you think of who will buy colourless glass at diamond prices? Or green glass at emerald prices? Conversely, not all jade is green, as I'm sure you know. And be it green or any other colour, all jade is not of anywhere near one single value. In all markets, it is the quality by appearance and the skill with which it is worked that determines end-user jade prices - and that scale is *very* wide.
> The FTC only regards nephrite and jadeite as jade.
> Jade is a gemological term, so you have to realize
> that you are dealing with people who stretch
> definitions quite a bit (who would assume that
> smoky topaz is actually quartz?)
As you should know, 'smoky topaz is a misnomer (*not* a synonym) and it is not a gemmological term. Also, I understand, that the US has agreed (under the Canute rule of recognising a futile exercise in arbitrary diktat) to relax its definition of jade to admit omphacite.
Jadeite and Diopside are at opposite ends of a solid solution series in the pyroxene group with Na and Al in isomorphous replacement.with Ca and Mg respectively. Under the lab harmonisation agreement, for the names Jadeite or Diopside to be applied to a sample from this solid solution series, the atomic constituency of the molecule is defined arbitrarily as >80% Na Al or >80% Ca Mg, all more evenly mixed being defined as omphacite, except for kosmoclor in which Fe replaces Al rather than Mg. In short and within your own argumentation, a sample can now contain <21% Jadeite and still be sold as Jade (Omphacite) in the US market. The lab harmonisation covers the major labs of IT,US,CH and TH and is likely to form the core of the CIBJO revision to the rules for jade that are presently in the making..
In reply to the OP, *some* serpentine can look like 'cooking grade' jade (usually nephrite) and is, in the Western tradition, considered a Jade simulant). It is discriminated from Nephrite and Jadeite by RI, SG. and texture.
So I understand, the Chinese word 'yu' means jade and has always carried a broader meaning than the English 'jade'. The Chinese were prizing and working nephrite for thousands of years before (relatively recently) they discovered the charms of jadeite through trade with Burma. To my mind there is no doubt that 19th century Western pedants would have reserved the trade name of 'jade' to jadeite alone, had not the cultural importance and precedence of the use of Nephrite as jade by the Chinese been impossible to ignore - however untidy and inconvenient it was to Western ideas of order and categorisation.
There's an apocryphal tale that illustrates the gap in Western and Chinese appreciation of 'jade-like' stones. With the gold-rush of 1849, westerners rushed to California to take the gold. When the Chinese came, in appreciable numbers, it was not for the gold, but for the californite, nephrite etc. that the western miners thought valueless. The Chinese community simply scooped up all the 'yu' it could find and shipped it quietly (and very profitably) back to China :-)
26th Apr 2013 18:02 UTCRock Currier Expert
26th Apr 2013 19:28 UTCDavid Von Bargen Manager
> greenish becomes jade.
I was referring to the time before knowledge of atoms and crystallography. Prescientific classifications (especially of gemstones) heavily relied on color. "Jade (Yu in Chinese pinyin) was defined as beautiful stones by Xu Zhen (about 58-147) in Shuo Wen Jie Zi, the first Chinese dictionary. " http://chineseculture.about.com/cs/history/a/JadeCulture.htm - so it fits into this earlier time frame very well.
The Chinese may have shipped back plenty of Yu when they stumbled over it, but they came for the gold. (they would have heard about the gold, but who would have told them about the jade?)
The smoky topaz is a term (mis)used for jewelry (I have never seen a mineral dealer offering it for sale as specimens)
AUTH. AND GIA CERT GENUINE ITALIAN SMOKY TOPAZ NECKLACE
http://mt.ioffer.com/i/auth-and-gia-cert-genuine-italian-smoky-topaz-necklace-37146331
You could probably also add ureyite to jade, but it is fairly rare http://www.minsocam.org/ammin/AM69/AM69_1180.pdf
26th Apr 2013 20:48 UTCPaul Brandes 🌟 Manager
You pretty much answered your own question Bill; they are two completely different minerals....
26th Apr 2013 22:43 UTCOwen Lewis
-------------------------------------------------------
> > When you classify things by color, everything
> > greenish becomes jade.
>
> I was referring to the time before knowledge of
> atoms and crystallography.
No. East or West, not all jade has ever been green. Conversely, West or East, not all 'greenish stones become jade'. To say so is to misunderstand the essential (pre-scientific but still extant) defining characteristics of jade. No one ever would or could have ever confused emerald with any jade. It is possible (without scientific testing) to confuse some serpentine and jade. Of the jade simulants, serpentine can be one of the better ones. It can indeed be Yu.
> Prescientific
> classifications (especially of gemstones) heavily
> relied on color. "Jade (Yu in Chinese pinyin) was
> defined as beautiful stones by Xu Zhen (about
> 58-147) in Shuo Wen Jie Zi, the first Chinese
> dictionary. "
> http://chineseculture.about.com/cs/history/a/JadeC
> ulture.htm - so it fits into this earlier time
> frame very well.
I think that supports all I have said. It also has nothing to say about colour.
> The Chinese may have shipped back plenty of Yu
> when they stumbled over it, but they came for the
> gold. (they would have heard about the gold, but
> who would have told them about the jade?)
The Chinese came ostensibly for the coolie work and not to stake claims which they largely left to the kwailo. No one showed them the Yu. They found it for themselves (as one is wont to do when breaking and hauling rock for coolie wages) - and no one noticed or cared when they took it away.
>
> The smoky topaz is a term (mis)used for jewelry (I
> have never seen a mineral dealer offering it for
> sale as specimens)
>
> AUTH. AND GIA CERT GENUINE ITALIAN SMOKY TOPAZ
> NECKLACE
> http://mt.ioffer.com/i/auth-and-gia-cert-genuine-i
> talian-smoky-topaz-necklace-37146331
It's hard to guess what might be going on there,without either the wording of the certificate or even a decent view of the stones. However, I don't think that any of the following can be seriously disputed.
- The GIA does not ever certify that quartz is topaz.
- Some (little) topaz is coloured dark brown by the irradiation of colourless topaz. Such irradiation may be natural or induced. This material is reported not to be colour stable (Nassau and others) and may lose colour with repeated exposure to sunlight.
- The artificial production results from particle bombardment that leaves the material 'hot' for some months. The GIA lab facility at Carlsberg is one of the few in the USA licensed by USG to test and certify artificially irradiated topaz as safe for public sale in the USA..
27th Apr 2013 00:10 UTCRalph S Bottrill 🌟 Manager
27th Apr 2013 03:15 UTCOwen Lewis
-------------------------------------------------------
> It's good to see gemmologists finally trying to
> get some scientific integrity in their gem names,
Gemmologists do (and always have) mostly use the mineral species' names. However it does not help when the mineralogists change some of their species' names almost as often as they change their under ware. As to varietal names, again it is unhelpful that the mineralogists:
- Refuse to recognise and regulate the nomenclature of varieties within species.
- Happily use the very varietal names that are not recognised in mineralogy.
- Blame anyone but themselves for muddle that results. :)-D
In some cases the mineral species names are not used in the gem trade where there is good readon. E.g. jewellers do not sell corundum but either ruby or sapphire. And the gem trade never uses the names of mineral solid solution series mid-members. One can sell a lady a pretty, apple-green, peridot brooch but one will never sell her a mid-member of the Forsterite-Fayalite solid solution series. Nor would she be in anyway better off were one to try and do so..
> but defining jade is a frightful one!
Yes. But it is not a mineralogical term. Thus, in this and a few other like matters, it is for the mineralogists to follow where others lead,. That said, we are all still caught in the cultural difference between the approaches to jade in the East and the West. The Chinese Yu simply does not equate to the Western concept of Jade. They mean different things and trying to equate them only leads to grief. Both have their place in the great scheme of things. However, recognising this is no excuse-making for those who, in countries regulated in the Western tradition, want to up their profit margins by selling this, that or the other rock as 'Jade'. If it is of sufficient quality (and it usually isn't) there will always be a market for it in the East as Yu.
>Most gem
> dealers have always been more interested in a
> pretty or evocative names than knowing what it
> really is.
Gemmology was born in the last century to apply scientific method to the correct identification of gemstones and organic gem materials and the differentiation of the naturally formed from the treated, the synthesised and the simulant. In short, it serves the jewellery trade in promoting fair dealing with its customers.. These aims are entirely different from from those of mineralogy that exists to serve the interest of mega-corporations and the gainful exploitation of natural resources..
> But trying to define jade as including
> omphacite is awkward because most pure
> mineralogists would realize that by normal
> classifications jadeite should really contain >50%
> of the jadeite molecule, and omphacite is an
> anachroism retained to please petrologists, but
> will probably be declassified by the IMA one day.
All very true :-) But we have, since well before the mineralogists changed their minds, subdivided the Albite-Anorthite series into six discrete varieties according to the Na/Ca percentages and there are other like examples too. As already said, what constitutes Jade may be of interest to some mineralogists - but it is not for mineralogists to determine.
> Calling something with 79% diopside jade may
> automatically increase the amount of jade in the
> world but doesn't really clarify things much.
I agree, I don't think it does so either. It either does too little or too much. The International Colored Stone Commission of CIBJO has the whole concern of what is jade and how its different treatments are to be categorised under root-and-branch review at this time and the new rules might be in place before the end of next year. Within national markets, sovereign states are free to to make what rules they wish. But, for international trade, it only causes difficulty, misunderstanding and irritation if there is not a single set of rules for international trade. In my view, it is more important to arrive at that single set of rules for international trade that it is to fret too much as to whether those rules reflect exactly one's own preferences.
27th Apr 2013 10:31 UTCRalph S Bottrill 🌟 Manager
I agree mineralogists do need to accept that varieties do have their place, but these need to be clarified, its not good enough to say that ruby is red and contains corundum, etc - we need chemical or colour limits, otherwise it looks like alchemy. Many varietal names do have a lovely ring with great history, but personally I think forsterite is a fine name, I'm not sure why peridot sounds any better. We are happy with rose quartz and pink diamonds and that is at least perfectly clear, and seems preferable to generating new names for new varieties of gems.
I agree jade is not a mineral term, its a name used historically for various tough hornfelsic rocks used for lapidary purposes, so trying to squeeze it into a mineral database is going to confuse everyone.
Agreed that gemmology exists mostly to serve the gem industry in preventing fraud, but im not sure that mineralogy is the preserve of the mining industry - they mostly rely on geology, chemistry and metallurgy; I think that mineralogy is largely an academic exercise.
The example of subdividing plagioclases into multiple "minerals" was always frustrating because in reality most plagioclase has a range of compositions - it can be labradorite in the centre, grading rythmically to andesine, oligoclase and even albite in the outer zones in many rocks. It seems so much more sense just looking at the dominant endmember.
We cannot stop mineralogists having an interest in jadeite, its a rare mineral forming an unusal rock; we dont care quite so much about nephrite which is mostly actinolite or other boring amphiboles. ;-) Whether we need to have a say in its nomenclature is debatable, but we are still pleased to see that some clarification of its mineralogy is happening, as its does not really seem to be good enough to say its mostly green, fine grained, tough and got the right RI and SG. Chemistry is fundamental in most mineral products and indeed most other products you can buy - you dont buy food just based on colour and texture. If its going to be defined it needs to be done in a manner that can readily be tested unequivocally, and mineralogy seems the obvious way to do this. Whether we get too pedantic about what pyroxenes, amphiboles and other minerals are included seems to be something needing careful discussion - maybe these other minerals may be deleterious or enhance the use of Jade - has this ever been verified? We dont want to sideline gemmologists at all but perhaps they should take more account of modern mineralogical methods when determining the nature of gem materials - wouldn't it boost their own status?
27th Apr 2013 15:11 UTCBill Cordua 🌟 Manager
28th Apr 2013 04:38 UTCOwen Lewis
Ralph Bottrill Wrote:
-------------------------------------------------------
>.... there
> is a big problem with inconsistent and awkward
> mineral nomenclature as you say - ask anyone, it
> drives us nuts. Its a problem with scientists not
> communicating well between different specialist
> fields and even worse with the general public;
> even in the one field - as my manager says that
> organising geologists is like herding cats! I
> guess its the classic blind men and the elephant -
> we all know a lot about very little and dont
> understand why everyone else does'nt go along with
> us. Usually the young scientist wants to make an
> impression by overturning the status quo, while
> the older scientists fight hard to protect it.
Well, if that is so, then mineralogy is most surely not the only discipline to be so affected.
"We trained hard, but it seemed that every time we were beginning
to form up into teams, we would be reorganized. I was to learn later
in life that we tend to meet any new situation by reorganizing;
and a wonderful method it can be for creating the illusion of progress
while producing confusion, inefficiency, and demoralization."
That's attributed for a Roman, dead to almost 2,000 years. Plus ca change...
For the specific we discuss - and as has been said before - the prime purpose of a nomenclature is to convey meaning and inculcate a sense of orderliness that promotes good, communication. Continual sub-division and name changing (e.g. within the tourmaline group) must be destructive of both to some extent.
> Geologists and petrologists mostly use
> nomenclature thats still in the dark ages. I
> suspect some crystal chemists think of it as an
> academic game, never mind how it affects anyone
> else. Too many amatuers ignore it all and use old
> or pet names. So trying to get agreement on
> mineral nomenclature is always going to be an
> exercise in frustration; somehow we need a better
> method of looking at mineral names using a wider
> group of people, including geologists and
> non-professionals. So I think I've criticised
> everyone now, including myself!
The measured criticism (of whomsoever about whatsoever) should always be taken in good heart. Hearing another viewpoint can only ever help develop one's own. And, just occasionally, it may be a necessary catalyst, triggering some change for the better.
> I agree mineralogists do need to accept that
> varieties do have their place, but these need to
> be clarified,
Amen to that. But as I see it only IMA is placed to do this. Without that steadying hand, gemmology is (1) too fragmented by national interests and (2) too in thrall to a jewellery trade ever-increasingly driven by marketing considerations. Your very point, I believe? :)-D
> ....its not good enough to say that ruby
> is red and contains corundum, etc - we need
> chemical or colour limits, otherwise it looks like
> alchemy.
It's an interesting example to pick. Let me run this by you for a reaction. Gemmology has to concern itself not only with what is now but also with gems fashioned even 2,000 years or more ago and the historical records of dealings with them over the centuries. It's only in the last 10% of this time that science revealed that several beautiful and very different looking gemstones all had the about 98% the same chemistry, i.e. were the same mineral species, corundum). To call all past, present and future rubies and sapphires as plain corundum would be true, in a very limited sense, but entirely unhelpful in trading that very small part of all corundum that has gem quality. To call that part 'gem corundum' might be better but would still be insufficient as the market has always valued differently the several colours of gem corundum, the main watershed being between the red and the blue varieties of gem corundum.
Having, in the light of the science, hived of red spinel that, for most of a couple of thousand years, had been mistakenly traded and prized as ruby, keeping the old trade name of ruby for the red variety of gem quality corundum makes good sense to me. Scientifically, it does not offend, because the modern label 'ruby' concisely describes transparent, relatively unflawed and unincluded and monocrystalline corundum in which c. 1-3% of the Al is isomorphously substituted by Cr .Go less than a 1% substitution and the stone shades into pink from red until eventually it is colourless. Go above around 2% and the the visual excitement of the red in ruby starts to diminish, acquiring a greyish cast that when about the 4% Cr substitution point is passed the stone, losing value all the time as the grey cast increases, becomes unsaleable as a high value gem. Thus, what a ruby must be and the limits of its being are reasonably tightly drawn and do not fight with the science, as can be seem in the following couple of paragraphs.
The other main colour for gem corundum is blue and this variety is called by its ancient tradename of sapphire. The chromophore responsible for the blue of sapphire and the the physics of that colour production are both entirely different from ruby. To create the most desirable blue requires the presence of both Fe++ and Ti++++ in the correct proportions to be trapped in the crystal lattice (not substituted for some of the Al in the corundum molecules as in ruby. In ruby, the Cr acts to produce an exciting red colour in the transparent crystal by a ligand field effect. In sapphire, the colour causing mechanism is an inter-valency charge transfer.
So what then of gem corundum that is neither red nor blue, for there is also some yellow, brown, green mauve, orange (padparadcha) etc. - and colourless. All except the colourless have their own combinations of chromophores that, with or without participation of a colour centre, also act to cause a particular colouration through a charge transfer effect. The naming convention is that all types other then ruby are considered to be sapphire but must carry their colour as a prefix, e.g. yellow sapphire, padparadcha sapphire, colourless sapphire etc.. The unmodified noun, sapphire, is reserved always just for the (historic) blue gem.
That leaves just one loose end that only now is finally being tidied up. What to call pink gem corundum and when does pink become red? The insider joke for many decades was, "Well, it depends on whether you are buying or selling!" And conservative practice was to call it pink sapphire, sapphire being of lesser value than ruby, all else being equal. However, as science finally yielded the precise causes of colour, it became quite clear that the pink is only a light coloured form of ruby. Turning this naming around has been slow because of trade resistance to the change but some major laboratories are now certifying all pink corundum of gem quality as ruby. To me, as to a growing body of others, this initiative is entirely logical and correct.
You will appreciate that the above has been a very quick skate through a topic area of some complexity and with which the general public and most of the gem trade are quite unconcerned. The bottom line is that we, the public, grow up to know that there are red and blue gems called ruby and sapphire. At their best, both are extremely beautiful and hard wearing but, as a generality, ruby costs more than sapphire of a similar quality. In the buying of a pretty bauble (and putting to one side for the moment considerations of treatments and synthetics), what else does does the average end-user gem buyer need to know? How would any of the guff above help improve the decision of which will please most as a present?
.
> Many varietal names do have a lovely ring
> with great history, but personally I think
> forsterite is a fine name, I'm not sure why
> peridot sounds any better.
Well, firstly, peridot is not forsterite :-) Forsterite (especially colourless forsterite) of gem quality is cut for the collector market (not the general market) and is sold under the name forsterite.. Secondly, as a gemstone, peridot has a history dating from biblical times at least. The use of precursor forms of the peridot name can be found in Roman writings. In English (or, more properly, in Norman-French) it may date from the early 13th C. and appears in modern English first in 1705. In short, peridot and other important gemstones were known, named, valued and traded long before minerals were identified and differentiated on a scientific basis.
If one rules out forsterite as technically inexact and as unnecessarily confusing to hundreds of years of precedent, what else *should* one call it that Joe Public will accept without blinking. For the trade and the gemmologists, the name 'peridot' carries a sufficiently narrow meaning for purposes of identification and the fair processing of sales.
> We are happy with rose
> quartz and pink diamonds and that is at least
> perfectly clear, and seems preferable to
> generating new names for new varieties of gems.
Though the application of historic trade names as varietal names does not jar with me (and I see some advantages attaching to retsaining such names), yes, I have a hearty dislike of attempts to hijack varietal naming with newly coined marketing terms. When this extends to the registering of such names to obtain in law exclusivity of use for purposes of commercial gain, I can , with many others, go ballistic. IMHO, there is no case for the application of modern trade names to varietal nomenclature.
> I agree jade is not a mineral term, its a name
> used historically for various tough hornfelsic
> rocks used for lapidary purposes, so trying to
> squeeze it into a mineral database is going to
> confuse everyone.
Agreed. The several mineral species are all databased in their own right and the muddle that ensues with what should or should be traded under the name of 'jade' is to mineralogy no more than a curiosity of general knowledge?
> The example of subdividing plagioclases into
> multiple "minerals" was always frustrating because
> in reality most plagioclase has a range of
> compositions - it can be labradorite in the
> centre, grading rythmically to andesine,
> oligoclase and even albite in the outer zones in
> many rocks. It seems so much more sense just
> looking at the dominant endmember.
I hold no brief for the gemmological (and totally arbitrary) division of the plagioclase series - other then to recognise that it exists and is not about to go away. Though I have tried quite hard, I have been unable to trace the author of or authority for these divisions, as presently accepted. Even taxing the time and interest of the gemmologically learned with much better access to prime documents of record than I have, has produced no answer more useful than 'lost in the mists of time'. It ain't *that* old; circa 1920's is my best guess. And this wretched scheme does not even encompass plagioclase that shows the quality of peristerescence, that is known to gemmologists as peristerite and which, by Na/Ca percentage, can lie anywhere in the albite-oligoclase-andesine-labradorite part of the plagioclase series.
>...... We
> dont want to sideline gemmologists at all but
> perhaps they should take more account of modern
> mineralogical methods when determining the nature
> of gem materials - wouldn't it boost their own
> status?
My heart is with you Ralph - and hence I hang out on Mindat to learn. But my head tells me that there is a real limit to the identification of a common purpose. Yes, some geology and some mineralogy is, in the view of many, a fundamental part of a gemmologist's rounded education. However the focus of gemmological expertise is centred on the interaction of e-m energy with gem materials and, most of all, that part of the spectrum of radiated energy that is visible to us. It's about what light does to gems and what gems do to light. A core interest in gemmology and side interest only in mineralogy? Then there is the whole study of gemstone inclusions. Essential to any real expertise in gemmology but a sideshow for the expert mineralogist?
But your basic point is sound. I don't think that a gemmologist can become expert in his chosen field without a grounding in the solid state physics and inorganic chemistry on which mineralogy stands full-square. If it is to have a future, gemmology needs to draw more on advanced testing techniques that observe and record behaviour at the molecular or atomic level. Not that older and simpler test methods will not continue to have a real place in the scheme of things. After all, mineralogists and most gemmologists do so love their Mohs testing, don't they ?:-)
28th Apr 2013 10:03 UTCD Mike Reinke
Thanks for your comments on plagioclase near the bottom of the last thread. I go to shows and buy l'il nubbin's of stuff like feldspar varieties, bring 'em home and eventually read up on them some. I tried to sort out sunstone/moonstone/peristerite/et ceteraite...and gave up, saying, 'oh, feldspar.' Amazing too, that the origin of the classification is lost in just, what, 90 years?! paper and ink are older than that...
Nice to see I'm not alone.
Mindat can be like comfort food.
28th Apr 2013 13:42 UTCRalph S Bottrill 🌟 Manager
The ruby discussion is an interesting one to me as pink corundums often show up locally and cause argument about whether it's ruby or sapphire, so I was most interested in the recent views you report. I quite agree, i usually call them pale rubies, but not all agree. Still, amethyst is amethyst whether it's pale or dark, though there must be a lower limit I guess. Emerald and citrine are others that cause arguments.
The peridot issue is something different though: AFAIK all peridot is forsterite or close to it, but not all forsterite is peridot. It's true that pure forsterite can be colourless but this is very rare, and fayalite is usually brown, red or black. Peridot usually contains 80-95% forsterite, giving it a nice green colour; any less forsterite, or more fayalite, and the colour becomes browner, and not so useful for gems. So yes we need both chemistry and colour to define peridot.
Regarding the plagioclase series, most of the series members were defined by the 1840's, but I'm not sure of the details - I'm surprised it's not in Mindat but hopefully we can fix that, it's interesting to have such info for common varieties. But peristerite is an interesting material that is actually an exsolution intergrowth of two different plagioclase feldspars, giving a Schiller effect. It's usually in the albite-oligoclase region, maybe including andesine. A similar Schiller effect often is found in labradorite, and this material can be called spectrolite but not peristerite. Both effects are due to miscibility gaps forming during slow cooling and incomplete recrystallisation. So peristerite can simply be considered a variety of albite with Schiller.
Some mineralogists do get a little pedantic about varieties, eg "chrome" cerussite can be bright yellow due to faint trace of Cr, and many would like to ban this name as its chemically near pure lead carbonate, but it's lovely, distinctive material and would make great gems if a bit harder.
Inclusions are one area where gemmologists certainly excel, along with ID of fakes, frauds etc.; some mineralogists focus on chemistry or structural studies, personally I am always interested in how it all forms geologically, but it's all fun. We do need to all keep working together and make sure we can all communicate properly, so we do need to all agree on mineral nomenclature, not leave it to a few crystal chemists to make all the rules, otherwise we will be all talking different languages, so I do wish the IMA well with this.
28th Apr 2013 14:29 UTCKeith A. Peregrine
Thanks,
Keith
28th Apr 2013 19:18 UTCOwen Lewis
-------------------------------------------------------
> Well, Owen we have totally hijacked Bill's thread,
> I hope he doesn't mind, but it has highlighted a
> number of serious issues with nomenclature that
> need to be discussed more widely. I think we agree
> on most things.
I think we do too, Ralph. But the conversation could run and run. Maybe one day, despite the distance that separates us, occasion will present to continue it far into the night as the candle burns lower and the level in the litre bottle drops to zero:-).
> .....Emerald and citrine
> are others that cause arguments.
Yes, but pretty well clubbed to death in other threads in this forum within living memory :-)
> The peridot issue is something different though:
> AFAIK all peridot is forsterite or close to it,
> but not all forsterite is peridot. It's true that
> pure forsterite can be colourless but this is very
> rare, and fayalite is usually brown, red or black.
> Peridot usually contains 80-95% forsterite, giving
> it a nice green colour; any less forsterite, or
> more fayalite, and the colour becomes browner, and
> not so useful for gems. So yes we need both
> chemistry and colour to define peridot.
Yes but, to my belief, the presence of a reasonable amount of Fe is essential to that bright green colour, ruling out pure forsterite. Too much Fe in the solid solution and the colour loses its attraction, sliding towards grey or brown. 'Gems 6th edn gives the optimal Fein isomorphous replacement of the Mg of forsterite as 12-15%, sitting within the range you suggest. The absorption bands in the spectrum of light coming from peridot are generally considered diagnostic for peridot, being quire distinct, due the the presence of Fe and centered at 493, 473 and 453 nm. This is one way of saying no Fe = no Peridot or (pure-ish) forsterite = no peridot. From the same basic requirement for the presence of Fe we reliably find a birefringence value for peridot of 0.34-0.38, whilst Forsterite is likely to be 0.33 (since the RI ranges well overlap, in this particular differentiation, the birefringence value is more important than are the RIs per se. Variance in SG (given a good balance) should be supportive in this differentiation but is not diagnostic. Look Mum, no XRD!
The mineralogist view that 'better than 50%' is good enough to call it as the series end member simply doesn't do for the gemmologist, because we know that for allochromatic gems, even a fraction of 1% +/- of a chromophore can have a marked influence on the colour and hence on the gem quality of a specimen. See our discussion re. percentage of Cr in corundum.
> .... peristerite is an interesting
> material that is actually an exsolution
> intergrowth of two different plagioclase
> feldspars, giving a Schiller effect.
Yup. It can be thought of as a plagioclase analogue of the moonstone variety of K-series feldspar (adularescence/adularia). Doesn't look quite the same though.
> It's usually
> in the albite-oligoclase region, maybe including
> andesine. A similar Schiller effect often is found
> in labradorite, and this material can be called
> spectrolite but not peristerite. Both effects are
> due to miscibility gaps forming during slow
> cooling and incomplete recrystallisation. So
> peristerite can simply be considered a variety of
> albite with Schiller.
You reinforce my point that the division of the plagioclase series according to 'khaki-brained' mathematical ratios is not only arbitrary significance and actually runs across the grain of optical phenomena that are of real significance. If I were king, I think I would classify the whole simply as plagioclase (handier than 'albite-anorthite series' and meaning the same thing) and then differentiate within the series by optical phenomena (peristerescence, labradorescence etc) and by colour. As things are, I see scientific method being used simply as a cloak of pseudo-learning and to no good end. However I am now preaching heresy and no doubt any trade worthies reading this are turning puce and reaching for their revolvers.
Spectrolite. Gemmologists apply this name as a synonym for labradorite of particularly fine quality (originally applied to the fine produce of just one area of Finland.
> We do need to all keep working
> together and make sure we can all communicate
> properly, so we do need to all agree on mineral
> nomenclature, not leave it to a few crystal
> chemists to make all the rules, otherwise we will
> be all talking different languages, so I do wish
> the IMA well with this.
Agreed.
Regards,
Owen
@ Keith,
Not to hog any more to of this bandwidth, I hope that the 'forsterite-peridot part of the above answers your questions sufficiently. If not, do please come back, maybe as a fresh topic.
28th Apr 2013 19:26 UTCBill Cordua 🌟 Manager
29th Apr 2013 00:09 UTCRock Currier Expert
I can see that after the amber article you are working on, there are a number of other articles in the wings that you can start on.
29th Apr 2013 03:48 UTCDoug Daniels
Bill-
If you have a deposit that's minable, looks like you've found your trade name for your product.
29th Apr 2013 14:20 UTCKeith A. Peregrine
Keith
29th Apr 2013 18:35 UTCOwen Lewis
30th Apr 2013 15:24 UTCRalph S Bottrill 🌟 Manager
>Yes but, to my belief, the presence of a reasonable amount of Fe is essential to that bright green colour, ruling out pure forsterite. Too much Fe in the solid solution and the colour loses its attraction, sliding towards grey or brown. 'Gems 6th edn gives the optimal Fein isomorphous replacement of the Mg of forsterite as 12-15%, sitting within the range you suggest. The absorption bands in the spectrum of light coming from peridot are generally considered diagnostic for peridot, being quire distinct, due the the presence of Fe and centered at 493, 473 and 453 nm. This is one way of saying no Fe = no Peridot or (pure-ish) forsterite = no peridot.
All True
> From the same basic requirement for the presence of Fe we reliably find a birefringence value for peridot of 0.34-0.38, whilst Forsterite is likely to be 0.33 (since the RI ranges well overlap, in this particular differentiation, the birefringence value is more important than are the RIs per se. Variance in SG (given a good balance) should be supportive in this differentiation but is not diagnostic. Look Mum, no XRD!
Well, Pure forsterite has a birefringence of 0.033, and the most Fe-rich is 0.042, so from the RI data peridot contains about 70-95% forsterite, a little wider than the composition range you give (assuming no other chemical components). Yes optics can be powerful, but it's hard to beat chemistry for defining minerals. Not so good for defining colour varieties of minerals like quartz, fluorite, etc though, but maybe they just need more study?
> You reinforce my point that the division of the plagioclase series according to 'khaki-brained' mathematical ratios is not only arbitrary significance and actually runs across the grain of optical phenomena that are of real significance. If I were king, I think I would classify the whole simply as plagioclase (handier than 'albite-anorthite series' and meaning the same thing) and then differentiate within the series by optical phenomena (peristerescence, labradorescence etc) and by colour. As things are, I see scientific method being used simply as a cloak of pseudo-learning and to no good end. However I am now preaching heresy and no doubt any trade worthies reading this are turning puce and reaching for their revolvers.
Well, that is getting heretical now but it's good we can all look at the same things and see something different. I recall once reading something from Goethe it think, trying to explain that a colour theory for light was more important than the wave or particle theories. Didnt quite click to me, but maybe you need to be a poet or artist? But to many of us chemistry is very critical to define materials.
> . Gemmologists apply this name as a synonym for labradorite of particularly fine quality (originally applied to the fine produce of just one area of Finland.
What do they call labradorite lacking any Schiller? Plagioclase I guess?
> Well, as already detailed the name peridot predates the use of olivine by many centuries Also of course, these days, olivine IMA recognised as a mineral group name. One (not completely accurate) definition of peridot is that it is the only gemstone member of the olivine group..
If we tried to use the earliest biblical etc definitions for gems and minerals we would all be totally confused; a lot has changed, basically due to chemistry. Most geologists and petrologists use olivine as a synonym of forsterite or peridot, though you wouldn't use peridot for a mm-sized grain, so yes peridot's basically a gemmy olivine.
> Maybe one day, despite the distance that separates us, occasion will present to continue it far into the night as the candle burns lower and the level in the litre bottle drops to zero.
:)-D yes someday hopefully!
30th Apr 2013 18:07 UTCOwen Lewis
-------------------------------------------------------
> > From the same basic requirement for the presence
> of Fe we reliably find a birefringence value for
> peridot of 0.34-0.38, whilst Forsterite is likely
> to be 0.33 (since the RI ranges well overlap, in
> this particular differentiation, the birefringence
> value is more important than are the RIs per se.
> Variance in SG (given a good balance) should be
> supportive in this differentiation but is not
> diagnostic. Look Mum, no XRD!
>
> Well, Pure forsterite has a birefringence of
> 0.033, and the most Fe-rich is 0.042, so from the
> RI data peridot contains about 70-95% forsterite,
> a little wider than the composition range you give
> (assuming no other chemical components). Yes
> optics can be powerful, but it's hard to beat
> chemistry for defining minerals. Not so good for
> defining colour varieties of minerals like quartz,
> fluorite, etc though, but maybe they just need
> more study?
No, no more study. I should just type more carefully. The values I gave should have been 0.033 and 0.034-0.038, respectively. There are very few gemstones that gave a birefringence so high as to be in the first decimal place, though Smithsonite and Cerussite spring to mind - and none that are commonly found as cut stones. The birefringence of forsterite and peridot is higher than that of most gems and can be spotted easily with a loupe.
> > You reinforce my point that the division of the
> plagioclase series according to 'khaki-brained'
> mathematical ratios is not only arbitrary
> significance and actually runs across the grain of
> optical phenomena that are of real significance.
> If I were king, I think I would classify the whole
> simply as plagioclase (handier than
> 'albite-anorthite series' and meaning the same
> thing) and then differentiate within the series by
> optical phenomena (peristerescence,
> labradorescence etc) and by colour. As things are,
> I see scientific method being used simply as a
> cloak of pseudo-learning and to no good end.
> However I am now preaching heresy and no doubt any
> trade worthies reading this are turning puce and
> reaching for their revolvers.
>
> Well, that is getting heretical now but it's good
> we can all look at the same things and see
> something different. I recall once reading
> something from Goethe it think, trying to explain
> that a colour theory for light was more important
> than the wave or particle theories. Didnt quite
> click to me, but maybe you need to be a poet or
> artist? But to many of us chemistry is very
> critical to define materials.
As said, the science in gemmology is heavily weighted to consideration of the interactions of radiated energy and the gem materials. To the point where it is that interaction more than anything else that determines whether or not any mineral is to be considered as a gem. And of the whole spectrum of energy radiation, that narrow part of the spectrum that our eyes are designed to detect unaided is the key sector. And within that narrow band of wavelengths, it is out eyes that react to changes in wavelength by causing our brains to sense minute spatial/temporal changes (= variations in energy levels) as a sense of colour. So, yes, gemmology uses science but is not in itself a science. It is essentially concerned with how things are seen to be. Its values are quintessentially human, whereas the values of mathematics stand outside of humanity or any other form of life.
But getting back to plagioslase... I imagine that a mineralogist might care to know the exact Na/Ca balance in a sample, but that knowledge will not help a gemmologist much, other that to place the sample within the five quite arbitrary divisions between the six names that gemmology chose (so we are told) to use but for reasons for reasons that elude me. Of what use is 'Bytownite'? And if Bytownite is struck down, why should any of the other four intermediary names stand with their arbitrary divisions? Dear me... this might be a mineralogist writing this ;-)
> > . Gemmologists apply this name as a synonym for
> labradorite of particularly fine quality
> (originally applied to the fine produce of just
> one area of Finland.
> What do they call labradorite lacking any
> Schiller? Plagioclase I guess?
Labradorite. Schiller may or may not be present.
Schiller is a word that, used unqualified, may confuse. It covers both the play of colour effect that can result from lamellar twinning and also the reddish-gold glow given to a colourless crystal by minute particles of native copper trapped in the crystal. Since both of these can occur around the arbitrary andesine-labradorite boundary in the Na/Ca mix, use the word 'schiller' in connection with such material and which effect is one supposed to be describing? I prefer only to use schiller in connection with the presence of colouration from native copper particles, qualifying it as 'copper schiller' to make my meaning plain and to use another word to label light inetrference patterns. But that's just me....
> > Well, as already detailed the name peridot
> predates the use of olivine by many centuries
> Also of course, these days, olivine IMA
> recognised as a mineral group name. One (not
> completely accurate) definition of peridot is that
> it is the only gemstone member of the olivine
> group..
>
> If we tried to use the earliest biblical etc
> definitions for gems and minerals we would all be
> totally confused; a lot has changed, basically due
> to chemistry.
Chemistry is what chemistry is; it does not change. Only man's comprehension of it changes. This strikes to the heart of whether it is in anyway wise or even useful to rush about renaming everything as comprehension grows (or fashions change?). Spellings change over time as sentiment or fashion change but the essence of the word and its meaning are retained.
There is no utility in a spelling change. The phonetic roots of a slew of words, such as 'man', 'cow' and 'honey' are older than the English language with roots lost in time (at least to me) somewhere with the illiterate Germanic tribes of pre-history.We have many, many, more words whose written root (and meaning) lies in the Latin of Rome, Peridotus (s) / Peridota (pl), being found in Roman Empire period jewellery. Peridot is a perfectly serviceable label so why change it? 'Forsterite' is simply another label of no intrinsic descriptive value. Re-naming all peridot as forsterite improves nothing, is less exact in (current) meaning and would be cultural vandalism to apply to the peridots placed in Cologne cathedral in the earliest days of the Holy Roman Empire and that are still there today, to be seen, enjoyed and to cause reflection of two thousand years of European history and culture.
If one wants scientific exactitude, beyond that that application of the label 'peridot' gives (to those who understand the words they use), then apply a chemical description sufficiently accurate for the purpose in hand. Excepting that it would reduce by one the number of words we need to remember, there really is no gain that I can see to losing the label peridot into the rag-bag catch-all of forsterite.
> > Maybe one day, despite the distance that
> separates us, occasion will present to continue it
> far into the night as the candle burns lower and
> the level in the litre bottle drops to zero.
> :)-D yes someday hopefully!
A pleasure as always, Ralph. :)-D
4th May 2013 15:17 UTCRalph S Bottrill 🌟 Manager
I understood what you meant with the RIs, as I said the numbers fit, allowing for some other minor substitution.
> the science in gemmology is heavily weighted to consideration of the interactions of radiated energy and the gem materials.
Understood, but the chemistry and structure are still fundamental to their understanding in any sort of material -based science.
I do appreciate the history and value of a name like peridot, and the world would be a poorer place if we lost the words jade, Rubellite, amethyst etc., as long as we also understand their fundamental identity is more than just a coloured stone of particular hue.
4th May 2013 18:36 UTCOwen Lewis
-------------------------------------------------------
> I do appreciate the history and value of a name
> like peridot, and the world would be a poorer
> place if we lost the words jade, Rubellite,
> amethyst etc., as long as we also understand their
> fundamental identity is more than just a coloured
> stone of particular hue.
Ah Ralph... we must be short of anything better to do this holiday long week-end. I assume that it is for you too way down under?
A name is a label. What constitutes an appropriate label depends on the purpose of the speaker and the audience. The general purpose is to convey information. Many things go under more than a single label and that probably includes both thee and me. In my case and at differing times, places and with different people, I have been called maybe some 20 or so other names than the two my parents gave me at baptism, Some of these have been terms of endearment, some disparaging and some signifying membership of or status in a group, e.g. 'Daddy'. One knows what is meant by them and learns to answer to them all as and when appropriate.
It's rather similar for mineral varieties I think. As you and I need to use our registered name for any legally binding act, for other purposes, it is oftem more informative to use some other name. Returning to Peridot, it has a chemical formula. Not a fixed one but one that can be sufficiently accurately described with symbols. However this is very unhandy for speech. I suggest that with the understanding that 'Peridot'~=(Mg,Fe)2SiO4
and knowledge of the limits of Mg isomorphic replacement by Fe, in speech and often in writing too, use of the label 'Peridot' is both convenient and sufficiently accurate.
Of course, one might choose some other label than 'Peridot' to convey the same meaning. Were one to use 'Forsterite' it seems to me that would be less rather then more accurate, since 'Forsterite' can't imply the particular limits on Mg/Fe substitution that are prerequisite to produce the green colouration (radiation absorption) that is essential to the gemstone we wish to describe. I suppose one could call it something like 'Forsterite A' to acknowledge both the underlying chemistry and Mg/Fe substitution within set limits, but why do so, when the ancient word 'peridot', in this scientific age, already carries the identical meaning that 'Forsterite A' (or similar) would carry? One surely is not adding to the communication of meaning but rather creating change for change's sake?
It seems to me that there is a broad underlying principle here that bears on a trend to constantly re-label things as knowledge advances and to the confusion of many. That one understands better of what something is composed does not, of itself, require any change in name, it seems to me.
4th May 2013 23:42 UTCRalph S Bottrill 🌟 Manager
I don't think we need to dispose of gem or variety names like peridot, I agree its useful, i was just asking that we recognize the value of knowing their chemistry as much as their colour, else all fine grained green rocks become jade, all cubic zirconia becomes diamond, etc.
5th May 2013 01:53 UTCOwen Lewis
6th May 2013 15:22 UTCDavid Von Bargen Manager
6th May 2013 23:22 UTCOwen Lewis
Extinction is of course directly relates to the Brewster angle and RI and, for plagioglase RI and SG, the relationships have been documented and widely published. Yet there are difficulties in resolving 'border disputes (esp. at the andesine/labradorite border?), probably because of the almost inevitable lack of purity in real-world specimens.
I have not yet found any convincing reason why the plagioclase series should be divided into six parts determined by an arbitrary mathematical ratio of Na/Ca and wonder again on what authority this was ever done?. If differentiation within the series is to be made, it seems to me better that the varieties follow the presence of natural phemomena, e.g. peristerencence, labradorescence and copper schiller.. But I'm wide open to reasoned persuasion.
7th May 2013 00:15 UTCAlfredo Petrov Manager
7th May 2013 01:14 UTCOwen Lewis
-------------------------------------------------------
> IMA approval for plagioclase names was not
> necessary, Owen, because studies of the series and
> use of the names pre-date the existence of the IMA
> (1959<). When the IMA was created, these names
> were "grandfathered".
I understand the general principle but:
- Bytownite was never approved by the CNMMN, of IMA, so I believe, and thus the division of plagioclase can't be truly 'grandfathered by IMA but must at least in part have been re-invented. Or did IMA simply have a 'black hole'? I hold no brief for the series of six species (now varieties) but what was the logic for IMA reducing it to five and for what purposes?
- What purpose was there ever (pre-IMA) in arbitarily splitting the series into five or six species?
If we cannot understand how it is that we arrive at where we are, how the Bill Hill can we best decide, rationally, where it is we should be going?
7th May 2013 01:14 UTCAlex Homenuke 🌟 Expert
It's kind of hot here in the Vancouver area today (Ralph), so I think I will grab a beer and watch some cartoons:)-D
7th May 2013 02:56 UTCAlfredo Petrov Manager
Owen, I'm not aware of the IMA ever having lost bytownite or having reduced the previous 6 members of the plagioclase series to 5. If bytownite did not appear on some list on which the other 5 plagioclases were present, that was probably just an oversight by whoever compiled the list and not some official ex cathedra decision. List compilers are human too. :-)
7th May 2013 15:45 UTCDavid Von Bargen Manager
Anorthite - (Na up to 4%)
Andesine (Na 5-8)
Labradorite - (Na 4-6)
Oligioclase - (Na 8-10%)
Albite - (Na 9-11%)
Bytownite - (Na 7.6%)
Dana 6th ed 1892
Anorthite - An
Andesine - Ab3An1 to Ab1An1
Labradorite - Ab1An1 to Ab1An3
Oligioclase - Ab6An1 to Ab3An1
Albite - Ab
Bytownite - Ab1An3 to Ab1An6
Tschermak did a lot of work on the series.Aventurine is a variety of oligioclase.
"What purpose was there ever (pre-IMA) in arbitarily splitting the series into five or six species? " They were not considered species even in 1892.
Between the isomorphous species Albite Anorthite, there are a number of intermediate subspecies, regarded as isomorphous mixtures of these molecules, and defined according to the ratio in which they enter ...
Danas 6th edition http://books.google.com/books?id=61IPAAAAIAAJ&printsec=frontcover&dq=danas+system+of+mineralogy+6th&hl=en&sa=X&ei=KxaJUYKaHMm98AGEmYGACA&ved=0CFgQ6AEwBQ
7th May 2013 19:21 UTCOwen Lewis
-------------------------------------------------------
> Owen, I'm not aware of the IMA ever having lost
> bytownite or having reduced the previous 6 members
> of the plagioclase series to 5. If bytownite did
> not appear on some list on which the other 5
> plagioclases were present, that was probably just
> an oversight by whoever compiled the list and not
> some official ex cathedra decision. List compilers
> are human too. :-)
True. But Mike O'Donoghue and Brian Jackson in 'Gems 6th Edn are categoric (see the entry for Bytownite). M'OD and BJ are, are you know, both luminaries. For the record, neither BJ (author of the latest 'Gems' chapter on feldspar and Principal Curator (Mineralogy) Museums of Scotland) nor Prof George Rossman (Berkeley Calif) have been able to identify any authority for the five (or six) name division of the plagioclase series (BJ by private correspondence and, according to GR from his own published papers, this is "lost in the mists of time".
None of which makes you mistaken Alfredo, but if others are mistaken, it's not a simple case of omission.
In any event, it's history for mineralogists, since only Albite and Anorthite are currently approved :-)
7th May 2013 21:05 UTCAlfredo Petrov Manager
7th May 2013 21:26 UTCDavid Von Bargen Manager
The nomenclature of feldspars is complex (Smith .. devotes 45 pages to it)
Smith, J. V. Feldspar minerals: in 3 vol. Springer.
When you start to look at the exsolutions of some plagioclase compositions, such as peristerites, Huttenlocher intergrowths, Bøggild intergrowths; things get complex.
7th May 2013 23:42 UTCOwen Lewis
-------------------------------------------------------
> > The nomenclature of feldspars is complex (Smith
> .. devotes 45 pages to it)
>
>
> Smith, J. V. Feldspar minerals: in 3 vol.
> Springer.
>
> When you start to look at the exsolutions of some
> plagioclase compositions, such as peristerites,
> Huttenlocher intergrowths, Bøggild intergrowths;
> things get complex.
That's a great quote, David. Isn't it just though? Don't anyone mention garnet!......
I've gone back to 'Gems' (6th edn - latest - published 2006) and also to my 2009 copy of the IMA CNMNC list of names. 'Gems' actually stipulates that none of the four intermediate members of the plagioclase series were IMA approved. Consulting the 2009, CNMNC 2009 listing of names, this seems to be correct, since the end members are annotated as 'Grandfathered' approved and the four other names (yes, all listed) are simply annotated as intermediate members of the plagioclase series Thus, while what is stated in 'Gems' may be technically accurate, it is, perhaps, splitting a hair.
Thank you very much for the references linking the six names in the plagioclase series back at least to the mid-19th C. However, if I understand correctly, the makeup of the members is differently specified. Why? At sight, I can't guess what the reason may have been from the proportions given. In any case, the "lost in the mists of time" origin of the 10/20/20/20/20/10 %ages seems to be a scheme of 20th C devising. It's not clear that this can have been for any reason of scientific improvement, though without understanding the basis on which the earlier 1850's and 1890's standards were derived, one can't really comment sensibly any further,
I checked also on the 2009 IMA status of Peridot. Not listed - even as an intermediate of the Forsterite-Fayalite series (both of which are given as Grandfathered). If there's a coherent pattern in all of this, I confess I have yet to spot it. There is now a reasonably tightly drawn scientifically based spec for the constitution of Peridot but none at all for the intermediate varieties of plagioclase, as they are have been defined in the last hundred years or so. Of what use and to whom are these arbitrary divisions of plagioclase? Why have they a place in the list when Peridot does not?
Ah well. sometimes one has to press ever deeper into the darkness before the light of truth eventually dawns, harsh though that light sometimes may be.
8th May 2013 07:48 UTCRock Currier Expert
8th May 2013 13:39 UTCOwen Lewis
Thanks to David, it's clear that the adoption of the six names, species or varietal, together with the knowledge that all six formed a solid solution series dates back at least as far as the 1850's which is getting close to the scientific beginnings of mineralogy and its whole nomenclature. Bytownite is named after Lt Col James By and the town he founded in 1826, Bytown, that grew to become Ottawa. Andesine was not identified until 1841. These dates imply that the division and naming of the plagioclase series almost certainly must have occurred in the narrow period of 1842 to 1858. We also know that when the six species/varieties were first differentiated it was not on the arbitrary basis applied later sometime in the 20th C. The 'why' of the series division remains a mystery.
As a gemmologist and with the gemmologically significant phenomena in plagioclase gaily waving two fingers at the arbitrary mineralogical divisions of plagioclase, I'm losing the will to chase much further..... To paraphrase a Pope sanctioning the massacre of all the inhabitants of certain villages, were they heretics or not, 'Call all plagioclase and have done. God knows his own'.
8th May 2013 15:12 UTCRob Woodside 🌟 Manager
8th May 2013 15:29 UTCDavid Von Bargen Manager
When you look at 19th century mineralogy, people were not only trying to classify minerals, but also determine what the best naming conventions were. A Linnean system was tried, but it prove=n to be unworkable. Different authors called the same mineral the same thing and a lot of people were naming incompletely characterized materials. We have to thank Mohs and people like the Dana's for straightening out the nomenclature (you can see this in the preface to the 6th edition)
"However, if I understand correctly, the makeup of the members is differently specified. Why?". It probably seemed to make more sense to equally divide them up in 20% increments as techniques became more accurate..
8th May 2013 15:39 UTCOwen Lewis
-------------------------------------------------------
> The why of the plagioclase divisions was surely
> that petrologists found it useful when looking at
> thin sections.
Rob,
That's an interesting thought. Might you expand on it? I can see it might explain one (but not both?) of the 19th C Dana-published divisions of the series. But hard to impossible to see it as rationalising the 10/20/20/20/20/10 %age division that at has persisted through the 20th C to the 21st C.
8th May 2013 15:49 UTCOwen Lewis
-------------------------------------------------------
> "However, if I understand correctly, the makeup of
> the members is differently specified . Why?".
> It probably seemed to make more sense to equally
> divide them up in 20% increments as techniques
> became more accurate.
But to what purpose? Maybe Rob has the key clue. Maybe we shall see.
Arbitrary division for its own sake would seem a nonsense.
8th May 2013 16:27 UTCDavid Von Bargen Manager
8th May 2013 17:27 UTCAlex Homenuke 🌟 Expert
The feldspars are very common constituents of igneous rocks and the calcium/sodium ratio essentially indicates where in the mafic to felsic continuum the rock belongs. If I remember correctly "Bowen's Reaction Series" also predicted the temperature of formation in relation to the chemistry of the plagioclase feldspars. All this is important for petrogenisis determination and economically for relation to mineral deposit formation. Today, the Ca/Na ratio might be commonly used but perhaps historically, as suggested by Rob, thin section characteristics might have led to the names being more commonly used. Thin sections were probably easier than chemical determinations compared to today.
8th May 2013 17:40 UTCAlfredo Petrov Manager
RI of the glass varies linearly with Na:Ca ratio.
9th May 2013 17:28 UTCDave Crosby
Somehow the human mind shuts down on seeing labels. "Wow! Must be true"
Thanks to all for a very lively and informative discussion!
10th May 2013 16:53 UTCOwen Lewis
-------------------------------------------------------
> The quickest and cheapest way to determine where a
> plagioclase specimen sits in the series is not
> chemical analysis but rather to melt a little
> fragment and measure the RI of the resulting glass
> bead.
:-)
SG is surely quicker and cheaper to test and also increments linearly with the mole % An ?
10th May 2013 19:31 UTCAlfredo Petrov Manager
(On Gemdat we'd probably advise people against breaking off bits of other chaps' facetted stones to melt for RI measurements, but this is Mindat :-D
10th May 2013 23:03 UTCOwen Lewis
-------------------------------------------------------
> SG is not very accurate, Owen, on small fragments,
> outside of professional settings. To get any
> decent degree of accuracy on the plagioclase
> series,
There's an article that needs writing on what is sufficient accuracy in an SG determination and why. I can't see it as a 'professional vs amateur' thing. One needs to understand what one is doing, what one expect to get out of it and then to equip and operate accordingly. Otherwise one is just playing games and, only too often, engaging in some exercise in wish fulfillment.
> ...an amateur would have to have a better
> balance than most possess, and use a relatively
> large specimen, make sure it's properly wetted,
> homogenous, recalculate for the density of the
> water at any temperature other than 4 C, etc.
Sad but true . As many do, I started out with a small scale only up to the job on a good day, downhill and with the wind behind it. But if one bides one's time, analytical grade balances come up regularly on e-bay when some lab is replacing its equipment, still in good condition and for around 10% (with a lucky snipe) of the cost of buying new. As for maths that is error-prone and slow to do manually - but set up a routine in a spreadsheet and one only has the bother once, after that all the calculations are fully automated (and with a permanent log of results). The water temp correction does have to be *watched* at every weighing but the adjustment figure only needs changing one or twice at most in a session of weighings, Getting and entering the adjusting figure is three extra mouse clicks :-)
If your balance is good for grams to the fourth decimal place, and one's methodology and setup is sound, sufficiently accurate SG determination for mineral/gem checking can be done with suitable samples that are down to 0.05ct in weight (0.01g). Opaque materials, aggregates and the porous are problematic but there ways deal with these too (some of the time).
> .... For
> a small fragment, the RI of the glass would be a
> faster and more accurate property to measure.
Please tell more, because I have not tried this. I shy away from it instinctively for the following reasons:
- I assume that the crystal must be melted (or at the point of melting) to change to glass. I understand the melting point of (say) Labradorite to be c. 1300 deg C. That's not a temperature that I'm equipped to work at.
- Plagioclase in monocrystalline form is anisotropic, i.e. it has three RI. Moreover not only do these RI change (not quite linearly) but the optic sign flips thrice (pos/neg/pos/neg and at known, consistent points) along the series as the mole %An rises. All that information is useful in determining that the material under test is indeed plagioclase and all that useful information is lost if one restructures the material as an isotropic glass If the RI of my glass is 1.544, do I have plagioclase glass or some other glass? Flip a coin?
- I think I'm unlikely to get an accurate RI - even less the alpha, beta and gamma - off my glass unless I first polish it carefully.
Or am I missing something here?
> (On Gemdat we'd probably advise people against
> breaking off bits of other chaps' facetted stones
> to melt for RI measurements, but this is Mindat
> :-D
:)-D
18th May 2013 16:03 UTCKathy L. Dean
Jade and Serpentine Comparison:
Nephrite and Jadeite:
Just About Everything - Jade, Jasper, Jaspagate, Hornblende, Serpentine, Quartz mixture and Unidentified:
26th Mar 2016 05:41 UTCIsaiah s.
26th Mar 2016 15:57 UTCRanger Dave
Synonym of: serpentine rock"
Then gives the formula for serpentine as; D3[Si2O5](OH)4 D= Mg, Fe, Ni, Mn, Al, Zn. If it has a lot of iron and nickle, it could be magnetic.
If you could post a picture I'm sure the experts will chime in.
Locally we have a lot of serpentine and one has a source of nephrite jade right next to it. (NEPHRITE JADE IN MARIPOSA COUNTY, Reprinted from Mineral Information Service (September 1966), By James R. Evans, Geologist, California Division of Mines and Geology)
Maybe someone can explain the association, if any.
26th Mar 2016 16:23 UTCTony Albini
Tony Albini
26th Mar 2016 16:42 UTCRanger Dave
26th Mar 2016 17:16 UTCDoug Daniels
26th Mar 2016 19:49 UTCOwen Melfyn Lewis
-------------------------------------------------------
.....
> serpentine is not jade, plain and simple.
Exactly so Doug - but minerals in the serpentine group are probably the jade simulants most often found in the marketplace.
26th Mar 2016 20:40 UTCKathy L. Dean
27th Mar 2016 00:18 UTCNathalie Brandes 🌟 Manager
Serpentinite is "A rock consisting almost wholly of serpentine-group minerals, e.g. antigorite, chrysotile, or lizardite, derived from the hydration of ferromagnesian silicate minerals such as olivine and pyroxene."
According to this publication, jade is “(a) A hard, extremely tough, compact gemstone consisting of either the pyroxene group mineral jadeite or the amphibole variety nephrite… (b) a term that is often applied to various hard green minerals; e.g. ‘California jade’ (or californite, a green compact variety of vesuvianite), Mexican jade (or tuxtlite, and also green-dyed calcite), saussurite, and green varieties of sillimanite, pectolite, garnet, and serpentine.”
So, sensu stricto to a scientist, serpentine or serpentinite is not jade. In the general market for ornamental minerals, however, people will refer to green serpentines and serpentinites as jade.
27th Mar 2016 02:00 UTCRanger Dave
The question is the connection. Why is the source of nephrite jade I referred to, and provided evidence that it is nephrite jade, associated with serpentine? Or did they just happen to form right next to each other?
27th Mar 2016 02:59 UTCDoug Daniels
27th Mar 2016 03:16 UTCKathy L. Dean
PS...Not going into any more details than that considering the volatile nature of the members here...LOL.
27th Mar 2016 03:32 UTCRanger Dave
-------------------------------------------------------
> Ranger - although I don't have any definite "this
> is true" connections, I believe the two are
> related. That is, jadeite and nephrite are often
> found in areas with
> serpentine("mineral")/serpentinite(rock). I could
> be wrong, and wouldn't be the first time....
That's what I'm trying to find out. There seems to be a connection, but I don't know if it's real or imagined. Both seem to have an actinolite connection.
27th Mar 2016 03:33 UTCRanger Dave
-------------------------------------------------------
> (tu)You are correct Doug...K.
> PS...Not going into any more details than that
> considering the volatile nature of the members
> here...LOL.
So true. I ask a simple question and they get very upset.
27th Mar 2016 03:43 UTCOwen Melfyn Lewis
Thanks for the interesting quotes. What is jade, on the global stage, is a bit of a mess, largely because the Chinese, to whom jade is historically and culturally important in a way never experienced in either North America or Europe, have and largely still do consider their use (pinyin) of 'yu' to be far more liberal that the quite arbitrary rules drawn up in the West for what may and may not be bought and sold as Jade.
However, for those who live in the West - or wish to trade with the West they are stuck with the following as items that may be traded as jade. What consenting adults choose to do behind their own closed doors is something else.
The term jade may be applied to any of the following:
- A mix of the two amphibole species, tremolite and actinolite with chemistry in the range of Ca2Mg5Si8O22(OH)2 to Ca2Fe5Si8O22(OH)2 . This material is known as nephrite and, when sold as jade is often referred to as nephrite jade. The end members of this series (> 90%) are not nephrite but sold under their mineral species names, lacking the essential physical attribute of toughness that first attracted people to nephrite jade. The optimal mix for nephrite is generally thought to be a 4:1 mix in favour of tremolite.
- Jadeite (or jadeite jade) is one end member of solid solution series jadeite-diopside, with the pure chemistry NaAlSi2O6.
- Omphacite. A recent addition to the western range of jades to assist coordination with the Chinese (pinyin) fei cui. Chemistry - (Ca,Na)(Mg,Fe2+,Al)Si2O6. Referred to as omphacite jade.
- Kosmochor. In the aegirine-diopside series. Another recent addition, often still called by its old name of maw-sit-sit. NaCrSi2O6
The list you give at (b) are all known jade simulants with some greater or lesser similarity in appearance to jadeite and omphacite. If and when offered for sale as jade under US and EU rules they are considered to be fake goods and legal sanctions can apply to the sellers. In practice, enforcement is likely to vary widely. Much genuine jade is of low quality and sells for modest prices only and this is where a lot of the fakes are found (think tourist trade in some countries) and enforcement is probably patchy. However for high quality worked items, the value can easily exceed USD 5,000 per *gram* and enforcement tends to be rigourous as no one likes to be swindled for large sums of money. This is as true for selling (e.g.) serpentine as jade as it is for selling zircon as diamond.
I don't think that the reworking of the rules for what is or is not jade has yet finished and we may see further change in the coming decade as we have in the last. In addition to a wish to better coordinate international rules, there is a practical problem of keeping identification sufficiently simple not to require a lab full of PhD physicists to check every piece offered for sale. With the rules as they presently are there is some difficulty with differentiation of some omphacite from jadeite by simple testing.
27th Mar 2016 04:21 UTCKathy L. Dean
27th Mar 2016 04:28 UTCKathy L. Dean
27th Mar 2016 04:39 UTCOwen Melfyn Lewis
Nice pics. Have you ever tested any of your pieces? What tests do you use?
27th Mar 2016 05:07 UTCKathy L. Dean
.
27th Mar 2016 05:18 UTCKathy L. Dean
-------------------------------------------------------
> I used 'Western' in the sense of the EU + North
> America.
>
> Nice pics. Have you ever tested any of your
> pieces? What tests do you use?
Sorry I misunderstood you; I should have read more carefully. I use every test known to humans, and some not known yet.
27th Mar 2016 05:50 UTCD Mike Reinke
Mike
27th Mar 2016 06:42 UTCRanger Dave
-------------------------------------------------------
> To Dave and Doug, there is an old article I have
> from Lapidary Journal, July 1974, that mentions
> jade and serpentine mixed at an deposit 7 miles
> west of Darrington Washington. The author was
> Lanny R. Ream. So, they do mix. Hop this
> helps...
Thank you. Maybe a member of the gem and mineral club I belong to has a copy I could borrow. Otherwise it's $10 on Amazon.com. I'm a seasonal national park ranger so money is tight right now.
One source, Univ. of Texas, has this to say; "... It [nephrite jade] is also found in association with serpentinite in all known localities." They did not say why.
Interesting.
Chromium, from what I've read, is what causes the green in jade. Chromium is also what gives the green/blue (I've even seen purple) colors to Mariposite, which is found about a mile north of the nephrite jade in Mariposa County, Calif.
Here's the whole quote; "Jadeite is a mineral that is restricted in occurrence to certain metamorphic rocks that have undergone metamorphism at high pressures but relatively low temperatures. Jadeite jade is found exclusively as nodular or lens-shaped masses in serpentinite. Nephrite jade, which is also a product of metamorphism (and fluid infiltration), does not apparently require the very special P-T conditions of jadeite and is much more widespread. It is also found in association with serpentinite in all known localities. Because of its extreme toughness in contrast to the weaker material it forms in (serpentine), jade is nearly always found as weathered boulders and cobbles in stream deposits or glacial sediment...." Source
27th Mar 2016 14:10 UTCOwen Melfyn Lewis
There is a problem though, testing the SG of opaque natural materials since in any one sample, one has no easy way of knowing what inclusion or voids there may be in the specimen under test. One way to avoid this difficulty when testing rough pieces is to test about ten samples from the same site (or even one sample broken into ten or more or more pieces). Results thrown off by large inclusions/voids will give outlier results and can be ignored; the remaining results (if nephrite) should all cluster in the nephrite range.
With a suitable refractometer and the polishing of a planar (for preference) cut and polished surface, RI measurements are a good way to separate nephrite successfully from almost anything else. the alpha and gamma must lie in the following ranges if a sample is not to be rejected of submitted for advanced testing:
- Alpha ray. 1.641-1.626
- Gamma ray. 1.615-1.600
Birefringence is usually on the range 0.26 - 0.28.
27th Mar 2016 16:55 UTCNathalie Brandes 🌟 Manager
I hope this helps.
27th Mar 2016 17:16 UTCKathy L. Dean
"A first check to differentiate nephrite from serpentine and other material is by SG. Nephrite should be in the range 2.90 - 3.10. If outside this range then its either substantially impure or or something else entirely."
Please refer to the picture(s) I posted earlier in this discussion on May 18, 2013 and yesterday March 26, 2016.
27th Mar 2016 17:30 UTCRanger Dave
-------------------------------------------------------
> The association of jade and serpentinite is due to
> the fact that both are formed in a similar
> metamorphic environment. A reference that
> discusses their formation and relationship in
> detail is: Harlow, G.E. and Sorenson, S.S., 2005,
> Jade (Nephrite and Jadeitite) and Serpentinite:
> Metasomatic Connections: International Geology
> Review, v. 47, p. 113-146.
>
> I hope this helps
Thank you. That paper contains a lot of words unfamiliar to a biologist, but I'll figure them out. Here's a link to a PDF of that paper: http://research.amnh.org/users/gharlow/IGR47n02Harlow.pdf
27th Mar 2016 19:03 UTCOwen Melfyn Lewis
-------------------------------------------------------
> Owen stated:
> "A first check to differentiate nephrite from
> serpentine and other material is by SG. Nephrite
> should be in the range 2.90 - 3.10. If outside
> this range then its either substantially impure or
> or something else entirely."
>
> Please refer to the picture(s) I posted earlier in
> this discussion on May 18, 2013 and yesterday
> March 26, 2016.
OK, Kathy I referred. With reference to your quoting of me as above, what should I conclude? Should we be discussing the testing of your stuff or would you rather we move on?
I think you are very fortunate to own and live on land in Oregon. I hear its truly beautiful country there - as is Northern California too. The nephrite deposits continue (and get larger) all the way up into Canada. I hear that the current commercial assessment is that British Columbia alone holds the world's largest known reserves of nephrite. Here's a link to a mouthwatering pic of nephrite - the sort of find that people dream of.... http://www.empr.gov.bc.ca/Mining/Geoscience/MINFILE/Jade/PublishingImages/jadepic3.jpg
27th Mar 2016 19:29 UTCKathy L. Dean
I'm totally lost by what you are saying. I was agreeing with you that the sg testing falls within what you quoted. I can assure you my testing is accurate, and I have no idea why you keep bringing it up.
Professor of Serpentineology
(not to be confused with snakes)
Entire Western United States
27th Mar 2016 20:44 UTCOwen Melfyn Lewis
27th Mar 2016 20:58 UTCD Mike Reinke
I got a pile of 70's LJ magazines from a thrift store, cut out the mineral articles, and tossed the rest. That was a rare find. Now if only I could find the last 10 years of MINREC that way!!
But wouldn't a hardness test suffice, since it is 4 compared to 6?
And wouldn't the serp. feel 'soapy'?
Just thinkin'..
28th Mar 2016 02:14 UTCAlfredo Petrov Manager
28th Mar 2016 03:36 UTCRanger Dave
-------------------------------------------------------
> Dave, thanks for the article. It'll take quite
> some time for me too.
> I got a pile of 70's LJ magazines from a thrift
> store, cut out the mineral articles, and tossed
> the rest. That was a rare find. Now if only I
> could find the last 10 years of MINREC that way!!
>
> But wouldn't a hardness test suffice, since it is
> 4 compared to 6?
> And wouldn't the serp. feel 'soapy'?
> Just thinkin'..
It's only a 6? I broke a sledgehammer trying to get a piece off a boulder the size of a coffee table. Didn't put a dent in the thing.
28th Mar 2016 04:07 UTCD Mike Reinke
PM me your address, I'll send a copy of that article.
I've taken a mash hammer to rocks in various dry stream beds around here, just to see what is there, and soon found how determined amphiboles are to 'keep it together.' So I let those slide now. There's not much of a chance that they hold good micros anyway.
28th Mar 2016 04:14 UTCMark Heintzelman 🌟 Expert
28th Mar 2016 13:48 UTCOwen Melfyn Lewis
-------------------------------------------------------
> Fascinating topic because coincidentally I'm
> currently in Hong Kong and last night was walking
> through shopping centers where an astonishing
> spread of jade qualities and prices are on
> display, ranging from emerald green jadeite
> pendants (and even "mere" cabochons) priced in the
> millions of HK$ (several 100,000 us$), down to
> stuff called "yellow jade" (chalcedony/carnelian)
> and "new jade" (all manner of utter rubbish
> including partially serpentinized volcanic rock).
> It is readily apparent that the word "jade" to the
> Chinese is not necessarily referring to any
> specific mineral species, and there is not
> necessarily any intent to deceive by calling
> something "jade". Luckily I was accompanied by
> Chinese friends who know their various jades very
> well and who were happy to point out to me exactly
> why one cab pendant could be priced at 2 million
> HK$ and the similar-sized one next to it a mere
> 600,000 HK$ just because of some slight difference
> in green tone that was imperceptible to my eye.
Yes, yes and yes again :-)
My understanding is that the pinyin 'Yu' is better translated as 'beautiful stone' rather than 'jade'. Certainly, in practice, much other stuff, including serpentine and varieties of chalcedony, is happily bought and sold as yu. This is a state of affairs that is very unlikely ever to change and why should it? It is Western thinking that has moved away from the Chinese cultural tradition that were largely introduced to the West as the time of Marco Polo.
Fei cui is the pinyin word applied to jadeite jade, and, as noted a few posts back, there have been, post 2006, serious efforts to bring together Chinese and Western thinking on what may be classified as fei cui/jade in a common, scientifically-based classification system.
Most of what I know that is useful about jade, I learned from a one-day seminar given by someone who had worked for over a decade in HK as a jade trader. His view (as a westerner) was that a science-based approach is all very well for the *identification* of jade against arbitrary standards but that it is of very limited use in the *valuation* of jade. He was further of the opinion that five years of evaluating, under supervision, much jade in six long days a week, was the minimum experience required to be allowed to make jade trades unsupervised. Most who try never get there. At the end of a one-day seminar, I was left with just an inkling of the size of a mountain of understanding (more than just learning) that I knew I would never climb.
28th Mar 2016 14:29 UTCReiner Mielke Expert
28th Mar 2016 14:55 UTCOwen Melfyn Lewis
28th Mar 2016 16:31 UTCKathy L. Dean
“Jade cannot be carved. Because of its hardness, it is said jade’s character is harder than steel, it can rarely be shaped by chiselling or chipping, but must be worn away by abrasion with tools and hard sand pastes. This is a process that requires immense patience, even with modern tools it remains laborious. Because the process was and is so labour-intensive and time-consuming, the stone so hard, jade symbolizes certain qualities and was embodied with human virtues: hardness, durability, constancy, purity, energy, grace and beauty.
Jade reflected the ability of a ruling elite to command resources, and therefore came to symbolize power, nobility, status and prestige as well as immortality and hence linking humans (especially higher ranking ones) to the spiritual world.
The mouthpieces of some opium pipes were made out of jade, due to the belief that breathing through jade would bestow longevity upon smokers who used such a pipe.
Jade’s basic color is white with a colorless opaqueness and a waxy like appearance. The variation of the colors comes from trace elements (i.e. iron, chromium, magnesia, calcium) within the stone’s chemical formula, creating a color range from various shades of apple green, bright green and spinach green, delicate violet tones, brown, grades of white, grey, red, reddish and brown tones, shades of blue to black, yellow, and orange.
Generally speaking, the value of jade is determined according to its color and the intensity of it, the lustre, texture, clarity and transparency.
Jades often have veins, blemishes and streaks running through them, though these may not always be regarded as flaws. On the contrary, some of these patterns are considered particularly valuable.
The so called ‘imperial emerald green’ color of the gem stone is the most expensive one. Because of the color range, jade has always been a perfect gem stone.
Jade was utilized for rituals and ceremonies, giving jade a sacrificial and religious character, and used as utilitarian jade for indoor decoration and personal adornment, hence limning the owner’s social status.”
28th Mar 2016 16:39 UTCReiner Mielke Expert
28th Mar 2016 17:14 UTCKathy L. Dean
28th Mar 2016 17:28 UTCReiner Mielke Expert
28th Mar 2016 17:37 UTCKathy L. Dean
I use water, and not oil as the lubricant, but the video shows how difficult it is to cut nephrite. The majority of my specimens are black nephrite jade of the size shown in this video, or larger. Nephrite eats through diamond lapidary blades like it’s candy! In fact, special blades are manufactured for cutting nephrite.
https://www.youtube.com/watch?v=PGZ-F72xEyw
28th Mar 2016 18:29 UTCReiner Mielke Expert
28th Mar 2016 18:32 UTCD Mike Reinke
The beach rock:
3150 pixels (12.4 Mpix) Edit
53E-493Amphibole Supergroup : AX2Z5((Si,Al,Ti)8O22)(OH,F,Cl,O)2
28th Mar 2016 18:47 UTCReiner Mielke Expert
28th Mar 2016 19:38 UTCOwen Melfyn Lewis
For those interested in the working of nephrite, including the CARVING of it, and have five minutes to spare, the following is well worth watching.
https://www.youtube.com/watch?v=qlgmEOjNCp0&ebc=ANyPxKq-dDluFsESXJUILBVS00Y_g3c9jeYeRRSwsWPcmr-hNK7RP0nC9bYpXlZsn9AVUFNm6i_Mr5XThHuU6_pvWk45YVtbhA
Many are confused between the meanings of hardness and toughness, imagining them to be synonyms; they are not.
A practical analogy works well for most people. A diamond is the hardest known natural substance found in any quantity - yet it can be smashed with a standard steel hammer because it not very tough. Use the same hammer with the same force on a thick piece of leather and the leather does not break. The leather is very tough but not very hard as it can be easily cut with a knife. Nephrite is the toughest natural substance known - but it can be tumble polished easily by other stones. A diamond crystal cannot be tumble polished.
Kathy, you talk of a 'diamond blade'. These are usually small pieces of bort sintered to some backing material (often steel) shapes as a disc. Similarly, nephrite is not a single amphibole crystal but a whole load of crystals running in different directions and *very* tightly locked together (rather as are the fibres in leather but much more so in nephrite).
When you run your 'diamond blade' against nephrite the bonds between the amphibole fibres are as tenacious or nearly so than are the bonds between the bort and the backing wheel. So your expensive 'diamond blade' quickly wears out, most of the bort particles having been pulled off it by the nephrite. This is why, in your video, Lyell is not using a diamond saw (good for cutting diamond) but a much softer tile saw (good for cutting ceramic tiles - or even nephrite).
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Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 25, 2024 05:36:06