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Identity HelpPossibly an emerald..?
24th Sep 2017 07:43 UTCAndrew Hinson
So I have this stone. I found it in a big barrel of raw minerals at a local shop yhat focuses on rocks, minerals, and fossils.
When I found it, the only "gem" showing is the bright bit on top, the rest was covered in black rock. I don't know what kind of rock. Actually, I don't think a few hours on Google and a couple of youtube videos qualifies me to know much of anything, so let's all just assume I know nothing at all...
After scrubbing (literally, with a sandsponge) the majority of the rock away, a six faceted green mass much larger than I anticipated when I started emerged. I took it to a local gem store that advertises cutting gems, and they refused to do anything with it while any rock remained and claimed that the stone is probably completely worthless.
That's fine, thought i, since I only played $5 for it. There's a clarity to it though, which the picture does not do justice. The stone is currently mostly covered in a yellowish crystal, but there's confirmed vibrant green underneath.
So basically what I'm here to ask is, if you were to give advice on how to remove the remaining black stone, clean off the discolored yellow crystal, and polish the (suspected but unconfirmed) emerald underneath to someone who knows absolutely nothing about gemstones and has a very limited budget, what would it be?
What are your thoughts?
24th Sep 2017 09:06 UTCErik Vercammen Expert
24th Sep 2017 10:31 UTCAndrew Hinson
I also am of the impression that amazonite isn't very clear, judging by the few pictures I've seen. This stone shows quite a bit of light through it, and has a few spots that look almost like fogged glass.
This is what it looked like before I started playing with it, if that helps at all.
24th Sep 2017 12:55 UTCAndrew Hinson
24th Sep 2017 14:29 UTCOwen Lewis
I don't think anyone here can suggest what your green stuff may be but, based on your pics and description, I think I'm safe in promising you that, should there be any emerald in your rock, it is of so poor a quality as to be worth no more that you paid for it.
If curiosity and the wish to learn drive you forward (applause!), you should approach someone like John Attard (a Mindat member) who will (for a fee) do an XRD quantitative elemental analysis for you. Emerald is beryllium aluminium silicate (colourless in its pure state), Emerald gets is colour from trace substitutions of Al by Cr (or V, in some schools). Either will in, trace amounts, cause beryl to colour green. Iron (Fe) can, in substitution for Al, also make beryl green but such green beryl (the most common type) should never be called emerald.
As a chromophore (cause of colour) in a colourless mineral such as beryl, Cr has some interesting properties. In particular, the UV in daylight will make it fluoresce. This means that the UV is not returned to the eye as expected but is down-converted to blue. This extra and, in nature, unusually strong visual appearance is what makes gem-quality emerald so valuable. Unfortunately, Fe is a much more common element; as a chromophore in beryl. It does not only itself fluoresce but prevents any Cr present from doing so either. Accordingly, it was shown conclusively some 20 years ago that the most visually attractive (and therefore the most expensive) emeralds are not those with the most Cr present in their make-up but those with *sufficient* Cr in their make up and with virtually no Fe also present to quench the Cr fluorescence.
I hope that this gives you a steer in the right direction in your pursuit of emerald. If you want to take study of your greenish aggregate further, as said, you need to start with an elemental analysis, such as XRD. As for physically separating the green from other coloured minerals AFAIK there is no way other than cutting it out.
As for amazonite, whilst this is almost always found as a translucent/opaque material, it is known to form near-transparent green-ish blue crystals at Luc Yen in Vietnam and, possibly, at other sites too.
Good luck with your chase after knowledge. Emerald is a fascinating place to make a start.
24th Sep 2017 17:29 UTCDonald B Peck Expert
Trying to identify a mineral from a photo is hazardous at best. You did supply a little more information when you said that a steel file did not scratch it. I am going to guess that Owen has already identified your mineral crystal for you. I think it is probably ordinary green beryl. It does not have the characteristic color of emerald. It does have the right color for ordinary green beryl. It is not transparent enough or blue enough to be called aquamarine (another variety of beryl). And, it is harder (and does not look like) than amazonite.
Don
24th Sep 2017 20:57 UTCPaul Brandes 🌟 Manager
1) It is almost impossible to ID a mineral simply based upon a photo. For some specimens, it's very obvious, but for something like this......
2) It does appear like a beryl, just not an emerald. Yes, it has a green colour, but not the vibrant green one would expect in an emerald. And, as Don also mentioned, your specimen doesn't have the correct colour for aquamarine or amazonite.
24th Sep 2017 21:14 UTCAndrew Hinson
I've borrowed my fiances phone, and this picture does it quite a bit more justice:
And you can better see the yellow I've been talking about, with bits of glassy green poking through.
Which gets us to the matter at hand;
My sponge won't polish it, my file won't scratch it. What would you finest of fellows suggest I use to clean it? I just want to expose the gem underneath!
24th Sep 2017 22:15 UTCKevin Conroy Manager
Here's a photo of a beryl that you can compare yours to: https://www.mindat.org/photo-189037.html. I think that you've cleaned it as much as it's going to clean up. The interior is going to look much the same as the exterior. The color may be a little more vibrant, but the likelihood of finding a portion large enough to be cut into even a small gemstone is extremely low. I would leave it as is, and enjoy it as a good sized beryl crystal.
24th Sep 2017 23:58 UTCOwen Lewis
You are repeating yourself and I shan't do the same. Emerald (in various languages) is a 2,000-year time-honoured name for fine, green , transparent gem. The only part of that description that fits the pics you show is 'green'. It might be worth what you paid for it but not a penny more. People - especially sellers - like to call their green beryl 'emerald' because of the status and extremely high prices fine emerald can command (to about USD 5K per *carat* for fine quality in over 1ct sizes). Ask yourself why you want to call your piece emerald and whether you should do so.
As comparators, here are a couple of pics of emerald. The colour of this first is fine (from Muzo, Colombia. However, it's value is ruined by a large and central pyrite inclusion and a large surface-reaching cavity on the pavilion (underside) and to the left of the pyrite. A lovely study stone though.
.
And below is an emerald on matrix from the Habachtal, Austria, the source of most of the emeralds of Ancient Rome. Small size and flaws in the crystal structure make this not a cuttable gem but all the emerald quality is there!
28th Dec 2019 11:53 UTCFiebre Verde
And below is an emerald on matrix from the Habachtal, Austria, the source of most of the emeralds of Ancient Rome. Small size and flaws in the crystal structure make this not a cuttable gem but all the emerald quality is there!
Owen,
I realize this is completely off topic (not even mentioning the delayed reply) but what makes you think Habachtal was the source of the emeralds of Ancient Rome? The scientific consensus is that most of the emeralds used in ancient Roman jewelry was traded to Rome from the Wadi Sikait and Gebel Zabara deposits, two of several Egyptian mines.
I know it has been speculated that the emerald deposit of Habachtal may have been known to the Romans and the Celts.
Problem is that the Habachtal deposit was not known in Roman times.
Emerald occurrence in Habachtal was first mentioned and described in the very late 18th century and formal mining started in the second half of the 19th century (1860s).
I realize this is completely off topic (not even mentioning the delayed reply) but what makes you think Habachtal was the source of the emeralds of Ancient Rome? The scientific consensus is that most of the emeralds used in ancient Roman jewelry was traded to Rome from the Wadi Sikait and Gebel Zabara deposits, two of several Egyptian mines.
I know it has been speculated that the emerald deposit of Habachtal may have been known to the Romans and the Celts.
Problem is that the Habachtal deposit was not known in Roman times.
Emerald occurrence in Habachtal was first mentioned and described in the very late 18th century and formal mining started in the second half of the 19th century (1860s).
A paper I am peer reviewing provides some clarifications to the early mining history of emeralds in Habachtal. This paper should be out next year - stay tuned!
Gérard
Gérard
25th Sep 2017 06:52 UTCAndrew Hinson
The situation is such:
1: I have a stone I cannot identify. We, as a group, have determined that it is probably not an emerald, and is definitely not an amazonite. It is likely a Beryl. I have never claimed it was an emerald, I merely believed it could be based on what I have seen other people claim to be emeralds on the internet. There was no malicious intent on the naming, merely ignorance.
2: Finding out what it is was a neat possibility, but not the intent of this thread. I asked if we could all assume it was an emerald for the sake of polishing and potentially facetting it, ONLY because it is such a hard material that my file and sandpaper are insufficient and my resources are near nonexistent in this field.
3: I have absolutely no intention of selling this, nor any delusions, now or ever, that it could be worth more than what I played for it. I did not know the market value of emerald, and did not care to know. This was never about money. I just wanted to polish the stone.
4: I like the stone, but I am not in love with it. I am not married to it. I spent $5 on it. If we misidentified it, it wouldn't break my heart. I would have learned a lesson and known better in the future. If we were right, I would rather get some practice now, on a cheap stone, than wait to try on an expensive one and potentially damage it.
5: again, this thread was originally posted in the prep forums because I wanted to know how to clean it. Learning what it is was secondary to that goal.
I am pretty bad at speaking and getting my point across. I do appreciate everyone volunteering to help, and I'm glad I had the opportunity to learn some stuff and now I can at least better tell the difference between beryl and emerald. Which is kinda neat. However, I didnt get the answer I was looking for, so I guess I'll head to the Home Depot and butcher the rock with stuff until I find something that works.
Thanks again for all your help, gentlemen. Sorry for the mess.
-Ash
25th Sep 2017 08:38 UTCIan Nicastro
25th Sep 2017 15:42 UTCOwen Lewis
Your thoughts on Brazilian emerald are interesting and worth following up.
Throughout recorded history, visually exciting green stones have been sought and traded under the name of emerald (or language equivalent) . These were not always a variety of beryl (though most were) and there were well-documented occurrences of:
- Chrome tourmaline from Brazil being traded honestly through Lisbon, as emerald in the 17/18th century.
- A suite of 'smaragd', gifted to the Roman Catholic church in medieval times, by the Holy Roman Emperor These were and remain displayed ever since then in Koeln cathedra but were proved, in the late 19thC to be peridot.
It was from a need, in the clear light of science, to improve the identification of valuable gemstones (mainly but not always or entirely by mineral species) and to clean up the nomenclature that the first gemmological association was brought into existence in the UK in 1931, to be followed quickly by the setting up of similar institutions in Germany, France, USA and then elsewhere. These bodies worked in harmony to develop a global set of standards to be relied on by the jewellery trade and the legal systems of the various countries. One such cooperative decision was that 'emerald' is defined as a variety of beryl, the primary chomophore of which is chrome, This arbitrary decision brought with it great clarity and simplicity in the certain identification of what is or is not emerald. Green beryl with no chrome == no emerald. Because of the very high price at which emerald can be traded, the need for strict control over the description of what can or cannot be lawfully sold as emerald brings clear benefits to end-user purchasers and helps keep trading honest.
All went well for some 50 years - until there was commercially significant new discovery of green beryl of saleable quality in Brasil. If this could be lawfully sold as emerald rather than as green beryl, the profit from trade in this would increase up to (say) ten-fold. An approach was made to the Gemmological Institute of America (by the 1990's being the authority for the world's largest precious stone market), to relax its rules for emerald identification and to permit any green beryl, whatsoever its primary chromophore, to be identified and sold correctly as emerald. The GIA decided to make this change, unilaterally, putting it at odds with gemmological institutes elsewhere in the world, creating uncertainty in the market - and making some traders *very* rich.
Traders in the 'recent' Brazilian and Zambian finds have been the great beneficiaries from this change. Co-incidentally, only last month, a dealer friend was kind enough to let me examine a 5 ct Brazilian emerald he was selling for close to GBP 49,000.00., Say USD 10K per carat. I only hope that my thoughts and sadness did not reach my eyes.
IMHO, this unilateral decision by the GIA opens a Pandora's box out of which several bad things have flown, such as;
- The selling of cr*p grade red beryl as 'red emerald'.
- A willingness by some traders to ignore other rules in gem nomenclature, leading us back to the uncertainties of the Middle Ages.
The IMA is, of course, silent on the meaning of mineral varietal names, leaving mineralogists (and all others) to rely (for gemstones) on the nomenclature and standards of identification as set out by the gemmological institutes, adopted globally by CIBJO, the good jewellers' international trade-governing body and the various national judicial systems when a precise meaning is required. This only emphasises the harm done by GIA in going its own way in relaxing the rules re. emerald; rules that it once was a wiling party to..
25th Sep 2017 15:43 UTCDonald B Peck Expert
Don
26th Sep 2017 02:49 UTCIan Nicastro
26th Sep 2017 07:17 UTCAlfredo Petrov Manager
26th Sep 2017 13:16 UTCHarold Moritz 🌟 Expert
26th Sep 2017 17:30 UTCOwen Lewis
Alfredo Petrov Wrote:
-------------------------------------------------------
> The value of a beryl to the consumer should depend
> on its colour, not its (invisible) chromophore.
Sorry, but that makes no sense to me. It is the 'foreign' chromophore transition metals that give beryl its typical range of colours. Thus, for the large influence that colour has on the value of any specimen, chromophores are the only determinable influence of inclusion-free beryl. It needs
- The presence of the right chromophore in the correct proportion.
- Where, as is often the case, there is a combination of chromophore elements present, the combined effect must not detract from the most visually exciting colour.
As regards emerald, the lid was ripped off the importance (or lack or it) of certain trace elements and which are found where and in what quantity in Le Huong's doctoral thesis, 'Microscopic, chemical and spectroscopic investigations on emeralds of various origins' 2008. There is a copy of this in the Mindat archive, I think, for any who wish to read it . Highly recommended; no summary here could do it justice. Just the barest key facts to help our our discussion are:
- Cr was found in all emerald samples tested. Cr levels in samples from Chivor are similar/lower that in the Brazilian samples tested. The highest Cr levels were found in material from Malipo, China.
- V levels were very low/nil at all locations except for Malipo, where one sample showed 0.597% presence as opposed to 0.011 - 0.082% in tests of material from all other localities tested. Only one lab has formulated V into its synthetic emeralds which speaks for itself as to V's contribution to emerald that will sell at a premium price. V does not fluoresce in daylight and the green it imparts is thus similar to green of Cr with its fluorescence quenched by Fe (the V green is also more yellow and less blue).
- Fe was found present in all natural samples tested. The lowest levels were in the Chivor samples and the highest from Malipo and several of the Brazilian localities tested. Chivor 0.02 - 0.15 %wr. Five Brasilian localities ranged 0.61 - 0.90 %wt - making Fe likely to be the primary chromophore in at least some Brazilian 'emerald' ;-)
It's fair to conclude that:
- The presence at trace level of V is of no importance in detemining by physical chemistry what should or should not constitute 'emerald'.
- The presence of Cr is essential to emerald but needs be at a modest level only. Of more importance than the absolute level of Cr is that the level of Fe, that near omni-present impurity, is only at a very low level.
> a beryl colored by V is of equal color to one
> colored by Cr, why should the Cr-colored one be
> priced higher? And if you say that Cr gives a
> better color than V (even though their spectra are
> quite similar), then again the price is, or should
> be, based on that superiority of color and not on
> the presence of the trace element. Incidentally,
> many emeralds have both Cr and V contributing to
> the green color, not just one or the other.
So please take a read of Huong's thesis and come back and hammer away with whatever facts you have to the contrary. Reduced to basics, the GIA story has been shot full of holes by a Vietnamese lady, studying at a German university. At its most crude and basic, the rule 'no Cr == no emerald' is a good one and should stand. It prevents the worst abuses in the emerald market.
> I'm
> not a big fan of the GIA in general, but they made
> the right decision to dethrone Cr as the only
> acceptable chromophore in this case.
Le Huong's immensely detailed study confirms that Cr is essential to the makeup of emerald. V is not essential. Fe is omni-present and the lower the Fe level the better the quality of the emerald.It is the absolute low level of Fe in a sample that makes emerald that causes the heart to go pitty-pat.
26th Sep 2017 21:05 UTCChris Rayburn
26th Sep 2017 23:01 UTCScott Rider
Here is a Harris Park, Colorado amazonite I just recently found (last weekend!). Its got the whispy white lines, albiet the color is different than yours and not quite the same, but it is a comparable piece.
26th Sep 2017 23:15 UTCAlfredo Petrov Manager
So was it the color or the Cr that gave the gem its value? This might be a trivial distinction to you, but to me it is fundamental to the reason gems have value at all - It's in their beauty, not their gem lab analyses. You will say that Cr is essential to the fine color, but it is still the color that gave value, not the Cr, which is why I think defining a gem name by its chromophore is semantic silliness.
27th Sep 2017 01:59 UTCDoug Daniels
27th Sep 2017 05:42 UTCFranz Bernhard Expert
Franz Bernhard
27th Sep 2017 15:37 UTCOwen Lewis
All the good arguments are not all on the same side, it seems to me. What one needs, surely, is simple rules that keep the market basically honest, with us all singing the same tune. It works like this. The spectra of Cr-coloured gens is diagnostic. In particular, there is a fine line doublet that is seen at 680 and 683nm. V spectra are similar to Cr but always lack this doubles. In well-made synthetics and the best natural stones (e.g. some ruby from Mogok) in which there is no or only vestigal Fe also present, the fluorescence caused in Cr by the UV content of daylight is clearly shown as the black lines of the diagnostic doublet are seen to glow brightly. I.e, at those wavelengths, the Cr is not absorbing light but is emitting red lightl. Where Fe is also present the doublet lines are black as expected for absorption lines. To see this requires only sample preparation (cutting), a suitable 'daylight' light source and a hand-held diffraction spectroscope.
Huong's work changed the game, showing convicingly that,
1. Cr is present in emerald from 35 of the main producing localities from around the world.
2. The most vibrant emerald green requires that no Fe be in the crystal.
3. Discussion of V is a red herring, deliberately or otherwise. It is sufficiently uncommon in emeralds to be ignored.
4 In the case of Brazil and also Zambia, Fe will usually have a major effect on the colouration and is likely, in some samples to be the primary chromophore.
27th Sep 2017 16:12 UTCOwen Lewis
-------------------------------------------------------
> Just curious: What does a synthetic beryl with
> some vanadium (and without Fe and Cr) look like?
> Can it be visually distinguished from synthetic
> beryl coloured by Cr (without Fe and V)?
> Franz Bernhard
As far as I know, that has never been done. There was a single producer (Pierre Gilson), who back in the 1970's/80's made synthetic emerald at least some of which contained V as well as Cr in effectual quantity. Of the two Gilson samples Huong tested, one had Cr at 0.305 wt% and with V at 0.113wt%. I.e there was significant V but Cr was still the primary chromophore. Fe in the Gilson samples was determined as nil or vestigal (similar to the five samples tested from Chivor, Colombia).
Pierre Gilson went out of business in the late '80's and his most interesting researches were bought up by Kyocera of Japan. To this day, they have continuing work based on Gilson's, though AFAIK no synthetic gem product from Kyocera enters the market. Apart from emerald, Gilson's excellent work included the best lapis lazuli, and opal synthetics.
28th Sep 2017 10:46 UTCAndrew Hinson
So that happened.
I'm told at the store I got it from that it's a Brazilian emerald. I picked up another one too, which I think is cute, and I'm going to display as it is since it's 95% grey crystal with an itty bitty emer... excuse me, Beryl sitting on top.
The original stone actually was pretty clear, but is pretty heavily included like you guys suggested it would be. There's a dime sized section I'm currently using a whetstone to shape. It's going to be really pretty, I'll show you when it's done!
28th Sep 2017 11:58 UTCEd Clopton 🌟 Expert
Other than cleaning off loose dirt and what matrix comes off voluntarily, I'd leave it alone as a good reference specimen of beryl.
28th Sep 2017 12:00 UTCAlfredo Petrov Manager
Presumably such Fe-colored "emeralds" are rather low quality/low value? When lighting mineral displays, I've noticed that minerals which get their green colour from iron (ludlamite and boracite, for example) look nice in daylight and under incandescent tungsten bulbs, but look a sickening greyish-green under fluorescent tube lights and "energy saving bulbs". I'm curious whether that also applies to Fe-coloured green beryls? (which, if so, would certainly make such gems look unappetizing in the average office setting)
28th Sep 2017 12:07 UTCOwen Lewis
28th Sep 2017 12:40 UTCOwen Lewis
-------------------------------------------------------
> Scott's photo looks like amazonite, which of
> course it is, but for what it's worth all of
> Andrew's photos look to me like beryl. I see no
> evidence of perfect cleavage, which feldspar
> should have, just sub-parallel fractures at an odd
> angle to the apparent axes of the crystal, and no
> perthitic texture. It gives the impression of a
> transparent mineral with lots of inclusions and
> flaws--a tiny particle between the inclusions and
> flaws would be transparent--which is
> characteristic of some beryl, rather than of an
> opaque-to-translucent mineral leaning toward
> transparency--even a tiny, pure particle still
> would be milky--which is characteristic of some
> amazonite from Viet Nam, Kola Peninsula, etc.
> There's probably a more concise
> mineralogical/gemological way to express that, but
> that's the best I can do.
I have seen just one small amazonite (sub-carat) from Luc Yen with strong colour more blue than green and only slight sleepiness (gem term for that slight and sometimes attractive lack of perfect transparency in an otherwise inclusion-free stone.
As (I hope) an illustration of your words re.an appearance in emerald of 'sub-parallel cleavage'
28th Sep 2017 16:43 UTCOwen Lewis
-------------------------------------------------------
> Owen, I'm intrigued by your last comment: "4 In
> the case of Brazil and also Zambia, Fe will
> usually have a major effect on the colouration and
> is likely, in some samples to be the primary
> chromophore."
>
> Presumably such Fe-colored "emeralds" are rather
> low quality/low value? When lighting mineral
> displays, I've noticed that minerals which get
> their green colour from iron (ludlamite and
> boracite, for example) look nice in daylight and
> under incandescent tungsten bulbs, but look a
> sickening greyish-green under fluorescent tube
> lights and "energy saving bulbs". I'm curious
> whether that also applies to Fe-coloured green
> beryls? (which, if so, would certainly make such
> gems look unappetizing in the average office
> setting)
Affredo,
You touch on an important gem topic.The neural excitement caused by the best gems is mainly about the way the material returns visible light to the human eye when illuminated by daylight (the band of energy radiation that our eyes have evolved to detect), Daylight from the sun is actually not a perfectly even distributor of all parts of the visible e-m spectrum (+ some UV and infrared). Viewing the visible colour spectrum of natural daylight displayed in a spectroscope, it is seen to be have many very narrow absorption bands (bits of the colour spectrum that have been absorbed by the Earth's atmospere).. This absorption is caused by the various gases and dust particles in the atmosphere.These absorption lines (absences) are known as the Fraunhofer Lines).
In the 19th C we discovered how to make 'pure 'daylight' by strong heating of metallic filaments and also by arcing. Suitably refined, both of these methods can emit visible light that has no missing or unevenly strong parts of the spectrum. Such light sources are perfect for the true display of all material where the assessment of its colour is critical to appreciation, value etc.. However, incandescent light sources have some draw-backs:
- They are relatively wasteful of power.
- They emit huge amounts of invisible infrared, that we sense as unwelcome heating.
- In the case of arc lamps, they also emit sufficient ultraviolet to pose an optical hazard (blindness) unless used with understanding, caution and, if necessary, protective measures.
In the 20th C, fluorescent and LED light sources were developed that overcome the problems of high power consumption and heating. They do however have a serious disadvantage. They do not emit evenly across the visible spectrum. There are many and large 'absorption' bands that cause false color rendition of objects illuminated by them, Over time, the quality of light output by both of these light source types has improved but none can yet match the purity and evenness of output given by the best incandescent sources.
To return to your question as to the effect of Fe. We all know that Fe alone can induce a green colouration into otherwise colourless beryl. We also know that where Cr is the primary chromophore, the additional presence of Fe (either ++ or +++) will affect the green tone of the specimen. It also affects directly the visual fluorescence of Cr+++ in the same crystal. But one needs to remember too that emerald is dichroic and the angle at which it presents to a viewer will change the perceived colour accordingly. This can usually be demonstrated clearly by rotating a specimen about x-y and y-z axes when illuminated only by linear polarised white light. This dichroic colour shift can be quite strong and the rough needs to be oriented correctly for best colour effect by a lapidarist, before he cuts the stone. Too late to say sorry afterwards :-) And there is also the quenching of fluorescence in Cr caused by the intimate presence of Fe+++.
Pricing and chromophore (purity of):
- Asking USD xx-xxx per ct for a small stone. If it's beryl and not resin-stuffed, of decent clarity and you like the colour, buy it and forget the rest - you're not being robbed. I'll guess that is over 80% of the trade by volume of sales.
- Asking USD xxxx(+). If you think you might ever have to re-sell (or your insurance company insists) get a reputable lab report. Truth is that sensible end-user buyers of emerald are still guided by their eyes. No matter what the hand waving from GIA (or anyone else) most current Brazilian and Zambian emerald sells only at a sharp discount to prices paid for fine Colombian and some Russian stones. The likes of us may know in outline the science behind this but most emerald end-users care only what looks best to them.
But then there are the dealers stocked with emerald from xxxx that they have to shift of else no turkey at Thanksgiving. Such dealers in 'Emperor's New Clothes have been around for centuries. Only the cajolements have changed, these days, to the likes of 'ethically sourced', 'no blood on them', 'not the tone/saturation of Colombian material but SO much better suited to the wonderful colour of *your* eyes' etc....
28th Sep 2017 23:07 UTCIan Nicastro
29th Sep 2017 00:57 UTCOwen Lewis
-- The most details study done to date shows that Cr is present in sufficient quantity to act as a chromophore in the beryl host.
- Almost all natural samples contained some Fe.
- The samples from Chivor Colombia showed Fe present at nil to vestigal quantity only. In samples from five Brazilian mines the Fe was present in greater quantity than Cr.
- Of the emeralds from some 27 sites around the world were quantitavely tested by LA-ICP-MS and EMPA. These included 5 specimens from Chivor and one each from five well separated Brazilian mines,
- V was detected in significant quantity only in the two samples from (Malipo China).
Do read Le Huong's doctoral thesis. If it's gone from the Mindat archive, you can download a copy from
https://publications.ub.uni-mainz.de/theses/volltexte/2008/1673/pdf/1673.pdf
Written only some nine years ago, the text is in english and is an eye-opener. It should be required reading at all the gem schools but it 'rocks the boat' and that is not welcome. However, AFAICS her study is in line with earlier work by Kurt Nassau and others scientists in the 1970s and 80s; just not in line with GIA's position. The author is now a a leading light in her nation's gemmological studies.
Returning this sub-thread to its origins, the old 'no Cr==no emerald' remains as good a basic ID guide as ever. Nothing that a hand,held spectroscope, decent incandescent light,dichroscope and polariscope can't sort out in minutes.Truth and good practice are not well served bu hose that abandon it for no more than colour shade matching.
Cr we must have. V is an also-ran and inconsequential. Fe kills the vibrancy in emerald.
29th Sep 2017 06:08 UTCFranz Bernhard Expert
Franz Bernhard
29th Sep 2017 18:06 UTCOwen Lewis
Indeed so. But all must have Cr as the primary chromophore, nicht war? And whether stones with more Fe than Cr should be sold as emerald is another unanswered question, it seems to me.
I've taken there thoughts across to the (near moribund) Gem-A forum to see if I can get any pointers to the studies that (must?) have preceded GIA's decision to break ranks in the '90s. If anything interesting transpires, I'll bring the links back here..
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