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Fakes & FraudsFake citrine
1st Oct 2012 15:35 UTCMario Hendriks (2)
Greetings Mario
1st Oct 2012 16:56 UTCRick Dalrymple Expert
1st Oct 2012 21:25 UTCOwen Lewis
1st Oct 2012 22:46 UTCWOLFGANG NOACK
regards
2nd Oct 2012 00:54 UTCWilliam W. Besse Expert
There is no production of naturally occurring citrine in Rio Grande do Sul, Brazil where these geodes are from. It is all enhanced by heat treatment.
The color depends several variables: composition of original stock, temperature they take it to, how long they leave it, etc. When talking to one of the producers down there, he said he had to test every mine because even if it looked the same as stock that worked it might not change well.
The better darker amethyst makes bad citrine because it is too dark. I saw them using material I would call quartz not amethyst because it was so pale but it made a beautiful golden citrine.
Bill
3rd Oct 2012 09:02 UTCRolf Brandt
3rd Oct 2012 11:39 UTCOwen Lewis
I'm unconvinced that all heat-treated Citrine can be successfully differentiated from the 'natural'. Remember that when Ametrine specimens first appeared - and largely because the locality of the mine was not disclosed - 'educated' opinion was that all Ametrine must result from treatment. This is now proven not to be so. However, this error should not be forgotten as it is a good example of some, claiming to speak with the authority of education and great experience, lacking the determinative powers they presumed to possess.
3rd Oct 2012 12:02 UTCSpencer Ivan Mather
3rd Oct 2012 12:44 UTCOlav Revheim Manager
All responses so far has taken for granted that this is a heat treated amethyst from Brazil. From the photo it appears to me that the color may be due to inclusions of Fe-oxides such as goethite. In such case the color may be natural, but it will not be a citrine.
Olav
14th Oct 2012 21:56 UTCTim Jokela Jr
Can anybody point to a significant locality for natural citrine crystals?
The gem experts suggest that the vast majority of faceted amethyst and citrine are synthetic nowadays, which explains the big tubs of flawless gems available at wholesale shows. Don't buy the facet rough if it's blocked out, only buy if you can see natural surfaces or crystal faces. Assume the citrine is heated, minimum.
15th Oct 2012 11:46 UTCRock Currier Expert
There are many localities that produce natural citrine. The new locality in Zambia that has produced the amazing japan law twins of citrine are just one of many. The pegmatites of Minas Gerais produce fine large crystals of natural citrine, sometimes weighing as much as 100 kgs or more) many of which have been cut into spheres. They more commonly produce smoky quartz crystals and sometimes smoky/citrine mixtures that you could call smoky or citrine depending on whether you were buying or selling them I guess.
15th Oct 2012 22:44 UTCDermot Walsh
best regards
dermot
i hope this appears correct.?
16th Oct 2012 13:13 UTCRock Currier Expert
16th Oct 2012 14:06 UTCDermot Walsh
16th Oct 2012 17:05 UTCCallum Elder (2)
Here in the mendips (somerset, UK) we have pretty much every quartz species/variation imaginable, and we do have natural citrine in geodes (sedimentary- weird but due to replacements in halite in triassic salt lakes) and also in hydrothermal quartz veins. It is obviously not the spectacular points you pick up in mineral shops (-fake) but small points normally in clear quartz. Decent citrine is rare however and its almost never like the heat treated stuff.
Callum
16th Oct 2012 17:14 UTCJesse Goodrich
I've been told by miners and the mine owners that unless you see a crystal come out of the ground yellow, assume it started out purple. The Brazillian mine owner who told me this said thats the only way he will sell something as citrine. Our store just sold and shipped to France, a large, pale yellow natural citrine crystal the size of an American football. It came from the mine i mentioned above, along with that little lesson.
In the world of gemstone beads, its expected that anything sold as citrine is actually heated amethyst. Unless it has a lab report to back it authenticity.
16th Oct 2012 22:19 UTCRock Currier Expert
Given how large the production of this material in these and the Brazilian pegmatites I would think that much of the citrine use in necklaces would be from natural citrine. Heated amethyst citrine usually has a rather distinctive look and I am sure that a lot of this kind of citrine is used in necklaces as well.
16th Oct 2012 23:15 UTCTim Jokela Jr
17th Oct 2012 01:38 UTCStephanie Martin
Here is a pair of single crystals from Russia, (with love :-D ), location Yakutia, Eastern Siberia, there are nicer ones in the gallery. These only set me back $5 each. The one label indicates Polar Urals but this is incorrect, it is Yakutia.
link to gallery showing citrine from Polar Urals:
http://www.mindat.org/gallery.php?cform_is_valid=1&loc=5547&min=1054&cf_pager_page=1
regards,
stephanie :-)
17th Oct 2012 04:28 UTCJohn M Stolz Expert
Here's another: The mine name was given as Alto de la Cruz
17th Oct 2012 12:36 UTCRock Currier Expert
17th Oct 2012 18:13 UTCAnonymous User
I'll post some pictures later.
18th Oct 2012 01:20 UTCAnonymous User
The larger cluster was bought from a Congolese man who said it was from the DRC. He suggested that all of the others that I had were also from the DRC, but looking at all of them together, it seems like the cluster is from the DRC, and the singles are indeed from Zambia.
The cluster is about seven inches across.
18th Oct 2012 04:41 UTCStephanie Martin
Sorry Ken, I don't know anything about the ones from Zambia or Congo, nice pieces though.
regards,
stephanie :-)
8th Jan 2013 01:02 UTCJason Evans
8th Jan 2013 13:08 UTCOwen Lewis
Citrine can also be produced by heating Amethyst.
8th Jan 2013 14:40 UTCAmir C. Akhavan Expert
Fe3+ is not a requirement for yellow color in quartz.
I do not know of any natural yellow quartz that is colored by iron built into the quartz lattice.
One could do a simple test:
1. dichroic + pales when heated => Al + irradiation (like smoky quartz) => citrine
2. dichroic + stays yellow or gets more red when heated => possibly Fe built into the lattice => perhaps citrine
3. not dichroic + stays yellow or gets more red when heated => inclusions of Fe-compounds => not citrine
Case 2 represents a possible case where dichroic minerals are included epitactically or with a preferred orientation (as in rose quartz - here I mean true rose quartz, not the one in crystals).
http://www.mindat.org/min-1054.html
8th Jan 2013 16:08 UTCOwen Lewis
9th Jan 2013 07:06 UTCDuncan Miller
9th Jan 2013 15:33 UTCOwen Lewis
-------------------------------------------------------
> but the citrines from Kongo are dichroic and hence
> not colored by iron oxide inclusions of the same
> type as in heated amethyst, which is not citrine.
> Fe3+ is not a requirement for yellow color in
> quartz.
> I do not know of any natural yellow quartz that is
> colored by iron built into the quartz lattice.
>
> One could do a simple test:
> 1. dichroic + pales when heated => Al +
> irradiation (like smoky quartz) => citrine
> 2. dichroic + stays yellow or gets more red when
> heated => possibly Fe built into the lattice =>
> perhaps citrine
> 3. not dichroic + stays yellow or gets more red
> when heated => inclusions of Fe-compounds => not
> citrine
>
> Case 2 represents a possible case where dichroic
> minerals are included epitactically or with a
> preferred orientation (as in rose quartz - here I
> mean true rose quartz, not the one in crystals).
>
>
> http://www.mindat.org/min-1054.html
Yes, Amir seems to be mistaken in this matter. It's not a mineralogy/gemmology spat but a matter of the correct scientific explanation of a cause of colour - and that is important. In 'The Physics and Chemistry of Colour. The Fifteen Causes of Colour' (Chap 5), Nassau K. sets out the explanation how transition element impurities cause colour change in a ligand field effect. Specifically, he discusses the role of Fe + heat in changing Amethyst to Citrine (colours) and also the colour reversion where Citrine + radiation can cause reversion to Amethyst.
I don't think there is any divergence of scientific view here. Citable primary source reports are many and, it seems, all one-way.
9th Jan 2013 20:01 UTCDuncan Miller
For example, how would one know if the illustrated dichroic, supposed "Congo citrine" bought in a large parcel of many kilograms of similar crystals from an African dealer is natural, heated, irradiated, or 'fake'? I suspect it is irradiated Brazilian material because it appears identical to such material which used to be sold by the late Jeff Graham in the USA as inexpensive faceting rough, but I have not yet come across any means of making sure. So what to call it, if not 'citrine'? Incidentally, many of the crystals have a thin blue band like the second one illustrated here. Anyone seen it before? Is it diagnostic?
9th Jan 2013 21:10 UTCOwen Lewis
-------------------------------------------------------
>.... If we are to
> know the precise cause of colour in any particular
> yellow quartz before we can name it, we would be
> hard pressed ever to call any yellow quartz
> 'citrine'.
>
> For example, how would one know if the illustrated
> dichroic, supposed "Congo citrine" ...... is natural, heated,
> irradiated, or 'fake'?
Is it Quartz? Y/N. If Y, then is it 'Lemon' or 'Citrine'?
What'a your view of dichroism in Citrine, Duncan? Is not all Citrine dichroic, albeit weakly because of the small birefringence of Quartz?
> ... So what to call it, if not 'citrine'?
Well, certainly not 'lemon':-)
I think we are of the same mind, Duncan.
9th Jan 2013 21:56 UTCAnonymous User
Quartz that is some shade of yellow, and the color is not imparted by surface staining or inclusions I can see with the naked eye is citrine. With no further information, there are no qualifiers to this term for me. "Citrine" means yellow, and if it is yellow, then it is some type of "citrine".
I understand that the yellow color could be caused by a number of factors.
Natural citrine is one that I have reason to believe acquired its color before it was taken out of the ground, by whatever means it was imparted.
If I don't use the qualifier "natural", it is because I have reason to believe was given its color by some means after it was mined. Of course the great majority of citrine out there is not natural (in color).
9th Jan 2013 23:03 UTCOwen Lewis
-------------------------------------------------------
> Since citrine is a trade name and not a
> mineralogical one, we are free (individually) to
> make our own definition.
Not really.'Oranges' and 'lemons' are 'trade names' for distinctive varieties of citrus fruit. Do you claim to be able to call an orange a lemon and to have others take you seriously? One has to 'go with the flow'. As to what the flow should be... we may agree that some regulation in the use of varietal names would be generally beneficial.
> Here's mine:
>
> Quartz that is some shade of yellow, and the color
> is not imparted by surface staining or inclusions
> I can see with the naked eye is citrine. With no
> further information, there are no qualifiers to
> this term for me. "Citrine" means yellow, and if
> it is yellow, then it is some type of "citrine".
'Some type'? What types are there? According to whom and with what recognition?
> I understand that the yellow color could be caused
> by a number of factors.
Would you care to state them? Not as a matter of personal opinion but the generally accepted scientific view?
> Natural citrine is one that I have reason to
> believe acquired its color before it was taken out
> of the ground, by whatever means it was imparted.
>
> If I don't use the qualifier "natural", it is
> because I have reason to believe was given its
> color by some means after it was mined. Of course
> the great majority of citrine out there is not
> natural (in color).
Fair enough :-)
I would only add that the cause of colouration may be the same, whether of geological or some man-made origin.
9th Jan 2013 23:54 UTCAmir C. Akhavan Expert
I would be really surprised if the British or any other gemmological society would ever adopt the citrine nomenclature for their approved trade names.
If the different causes of yellow color merit a nomenclature that reflects the differences from a mineralogical point of view is a different matter. I think it does.
EDIT: >also the colour reversion where Citrine + radiation can cause reversion to Amethyst.
This does not work with heated amethyst that turned deeply yellow (iron oxide formation at high temperatures).
It may work for those case where mild heating has led to the paling of the amethyst color centers, revealing an already present and previously masked faint yellow color by either interstitial Fe or iron oxides.
10th Jan 2013 00:30 UTCAmir C. Akhavan Expert
Yes, if you exclude eisenkiesel, no, if you follow the gemmologists definition (that does include it).
The small birefringence of quartz does not help, otherwise it would be always dichroic for transmitted light. Like putting a rock crystal on a yellow piece of paper and rotate it and see if the yellow changes - the way birefringence works, that doesn't make sense (and of course does not happen).
10th Jan 2013 06:11 UTCDuncan Miller
1. Should all yellow(ish) quartz be called 'citrine', irrespective of colouring agent?
2. Is all citrine dichroic?
3. Should varietal names differ in mineralogical and gemmological usage?
4. Is there any prospect of some regulation in the use of varietal names?
5. Is 'lemon quartz' citrine?
6. How can the various different colouring agents and treatments of yellow(ish) quartz be determined?
7. How should the various different colouring agents and treatments be designated - do they require distinct terminology?
8. Does so-called 'Congo citrine' actually come from the Congo or is it irradiated Brazilian material?
9. What causes the colour zoning and blue band in (some) so-called Congo citrine?
10. Are 'treated' and 'fake' synonymous?
10th Jan 2013 12:27 UTCSpencer Ivan Mather
Spencer.
10th Jan 2013 13:48 UTCOwen Lewis
-------------------------------------------------------
> How do the three cases distinguished above by me
> conflict with anything the cited authors say?
Rather then going round to loop again, may I restate more directly my original query. What do you say that the cause(s) of colour in Citrine are and what is/are the authoritative source(s) of this information?
> I would be really surprised if the British or any
> other gemmological society would ever adopt the
> citrine nomenclature for their approved trade
> names.
There seems to be an underlying misconception here. Beyond encouraging their autonomous memberships to use terms such as X or Y, the various gemmological associations can have no effect on the currency of any trade name. Trade names are market-led and, ultimately, their currency is a matter of popular sentiment. CIBJO maintains a list of names that the its jewellery trade members are encouraged to use but this is ultimately without authority.
Trade names are frequently adopted as varietal names but sometimes not. Some trade names are ancient and honoured by time, such as Ruby and Sapphire and have become true varietal descriptors. Others such as Tsavorite and Merelani Mint are simply 'me-tooist' attempts to enhance market share through 'branding'. Such (in my view) do not warrant varietal descriptor status. Both of these Garnets equally being Green Grossular (from E.Africa). Green Grossular seems a perfectly adequate varietal descriptor. The current trend to register gem tradenames for naturally occurring gemstones and then restrict the use of such names, as intellectual property with associated rights limiting the use of such a name to its owner, is to be deplored deeply and, in my view, should be discouraged by every means.
For discussions such as the one we engage in, I think the use of the term 'trade name' confuses rather than elucidates. Perhaps we should stick with terms such as 'varietal name' ' varietal descriptor' or even simply 'variety'?
> If the different causes of yellow color merit a
> nomenclature that reflects the differences from a
> mineralogical point of view is a different
> matter. I think it does.
May we first agree the cause(s) of yellow/golden/orangeish colour in Quartz, aka Citrine?
> EDIT: >also the colour reversion where Citrine +
> radiation can cause reversion to Amethyst.
> This does not work with heated amethyst that
> turned deeply yellow (iron oxide formation at high
> temperatures).
> It may work for those case where mild heating has
> led to the paling of the amethyst color centers,
> revealing an already present and previously masked
> faint yellow color by either interstitial Fe or
> iron oxides.
That Citrine + radiation *can* result in Amethyst is generally accepted and is authoritatively published in Nassau's 'The Physics and Chemistry of Color. The Fifteen Causes of Color'. Though he was a research scientist of some standing himself, Nassau cites over a dozen primary sources in respect of the colouration mechanisms found in Quartz that he outlines and says that there are 'over a hundred more'.
10th Jan 2013 14:37 UTCOwen Lewis
-------------------------------------------------------
> > Is not all Citrine dichroic, albeit weakly
> because of the small birefringence of Quartz?
> Yes, if you exclude eisenkiesel, no, if you follow
> the gemmologists definition (that does include
> it).
> The small birefringence of quartz does not help,
> otherwise it would be always dichroic for
> transmitted light. Like putting a rock crystal on
> a yellow piece of paper and rotate it and see if
> the yellow changes - the way birefringence works,
> that doesn't make sense (and of course does not
> happen).
You are right in that pleochroism is primarily an absorptive effect (onset of senility!). What is true is that in crystals where there is no birefringence there can be no pleochroic effect, an anisotropic state being a prerequisite. The presence of colour (absorptive effect) is second pre-requisite for pleochroism to be manifested.
AFAIK, gemmology does not concern itelf with Eisenkiesel (not a Quartz of gem quality) out of all the mineral species, gemmology only concerns itself with about 325 species, solid solution mixes of the same and a few rocks. This limited number increases to 500+ where differentiated gem varieties of these species are counted separately.
10th Jan 2013 16:04 UTCDon Swenson
12th Jan 2013 14:03 UTCOwen Lewis
-------------------------------------------------------
> This thread has raised several interesting
> questions.
Yes, it has.
>It may help to specify them.
> 1. Should all yellow(ish) quartz be called
> 'citrine', irrespective of colouring agent?
There's actually more than one issue here I think.
- Is there more than one cause of yellow colouration throughout a single crystal of quartz? Nassau and others say 'No'. I have read claims that lemon quartz is produces by irradiation but have not read a substantiation of this.
- Is all such quartz to be called 'citrine'? Webster (gem) and Frondel (min) - and other pundits - say 'Yes'. You agree and so do I. The term Lemon Quarlz seems to be imprecise and a seller's nit-pick'. A similar situation exists with yellow beryl/heliodor.
- Quartz coloured yellow by some surface staining or other treatment cannot be citrine, in my view. Rather it is 'yellow-stained' rock crystal.
> 2. Is all citrine dichroic?
I don't know :-) The two prerequisites for pleochroism are anisotropy and colour. However, not all specimens of such crystals will demonsrate pleochrism - at least at the levels where it can be detected by the human eye assisted by a dichroscope (let alone to the unassisted human eye). Isn't this the reason why the determination of pleochroism is considered a secondary test in in identification rathet than a primary one?
> 3. Should varietal names differ in mineralogical
> and gemmological usage?
I would think not. Let the marketeers go and conjure new names at will. But the very concept of variety within a species is not in accord with the molecular structuralist principles that are the foundation of modern mineralogical thinking. This leads the IMA to decline to rationalise varietal naming. It also leads some sensible gemmologists 'de facto' and quietly to ignore mineralogical nomenclature in a few specifics.
> 4. Is there any prospect of some regulation in the
> use of varietal names?
Not that I can see. Though, like you I would very much like to see this come about.
> 5. Is 'lemon quartz' citrine?
I think so. See above.
> 6. How can the various different colouring agents
> and treatments of yellow(ish) quartz be
> determined?
Surface staining, other surface treatment, Ferric iron in a ligand field effect.
> 7. How should the various different colouring
> agents and treatments be designated - do they
> require distinct terminology?
See above.
> 8. Does so-called 'Congo citrine' actually come
> from the Congo or is it irradiated Brazilian
> material?
Who knows? Remember Congo red andesine?
> 9. What causes the colour zoning and blue band in
> (some) so-called Congo citrine?
?
> 10. Are 'treated' and 'fake' synonymous?
Surely not? At least not so for most of the time. Treatment frequently just completes some process begun in the earth. Such treatment may be indistinguishable from the same process which has occurred geologically. A sapphire produced by heating Corundum that contains traces of Fe+Ti results in a sapphire as real as one taken from the earth. An oiled emerald is as real as one that is unoiled. Synthetics are also real and therefore cannot be called fake. Fakes are imitations by some other substance, e.g. where a white sapphire or glass is passed off as diamond. By definition a fake cannot ever be real.
13th Jan 2013 15:13 UTCDuncan Miller
I would never consider externally iron-stained colourless quartz as citrine. When discussing colouring agents, I mean those affecting absorption within the crystal.
Indeed, I did have the 'Congo red andesine' debacle in mind when querying the origin of 'Congo citrine'. Has anyone else noticed the dark lateral zoning and faint blue band I illustrated above? I have no idea how the blue band could arise, either naturally or by artificial irradiation, but it is there, in more than one specimen.
Duncan
13th Jan 2013 17:55 UTCOwen Lewis
-------------------------------------------------------
> I would never consider externally iron-stained
> colourless quartz as citrine. When discussing
> colouring agents, I mean those affecting
> absorption within the crystal.
Likewise.
> Indeed, I did have the 'Congo red andesine'
> debacle in mind when querying the origin of 'Congo
> citrine'.
I am grateful that, in the main, gemmology does not overly concern itself with locality of origin, only the authenticity of claims in respect to the substance. .
> Has anyone else noticed the dark
> lateral zoning and faint blue band I illustrated
> above? I have no idea how the blue band could
> arise, either naturally or by artificial
> irradiation, but it is there, in more than one
> specimen.
A commonly attributed cause of blue in quartz set out as follows on www.minscocam.org:
====
What causes the blue color in quartz?
The blue color in quartz results from Rayleigh scattering in the quartz ( similar to why the sky is blue). If you have a thin slab of the material, it will be blue in reflected light, while it will be orangeish-brown in transmitted light.
In studies of blue quartz from the Llano uplift in Texas, inclusions of rounded ilmenite with a diameter of 0.06 mm at a concentration of 125 per cubic micrometer were found by TEM. A similar type of quartz was also present in the Roseland district of Virginia. ( see Zolensky et al 1988 American Mineralogist pp313-323)
There have been some synthetic blue quartz colored by cobalt or iron, but these are not known to occur naturally.
====
Without having tested it, that sounds pretty interesting to me.... though I think the unit of measure might be um rather than mm, as given.
14th Jan 2013 19:19 UTCAnonymous User
-------------------------------------------------------
> Ken Ceglady Wrote:
> --------------------------------------------------
> -----
> > Since citrine is a trade name and not a
> > mineralogical one, we are free (individually)
> to
> > make our own definition.
>
> Not really.'Oranges' and 'lemons' are 'trade
> names' for distinctive varieties of citrus fruit.
> Do you claim to be able to call an orange a lemon
> and to have others take you seriously? One has to
> 'go with the flow'. As to what the flow should
> be... we may agree that some regulation in the use
> of varietal names would be generally beneficial.
Oranges and lemons are common names for different species of Citrus, and within each there are a number of varieties. But I nitpick.
Since we are discussing the use of a gem trade name, not a mineral species name, then my opinion is just as valid as anyone elses. You don't have to agree with it. Who regulates gem trade names? Anyone?
>
> > Here's mine:
> >
> > Quartz that is some shade of yellow, and the
> color
> > is not imparted by surface staining or
> inclusions
> > I can see with the naked eye is citrine. With
> no
> > further information, there are no qualifiers to
> > this term for me. "Citrine" means yellow, and
> if
> > it is yellow, then it is some type of "citrine".
>
>
> 'Some type'? What types are there? According to
> whom and with what recognition?
This was intended to be a summary of what I thought was previously known. Types? Manmade yellow quartz, natural yellow quartz with natural color, and natural quartz with induced color.
>
> > I understand that the yellow color could be
> caused
> > by a number of factors.
>
> Would you care to state them? Not as a matter of
> personal opinion but the generally accepted
> scientific view?
Again, I'm refering to what others said in previous posts.
>
> > Natural citrine is one that I have reason to
> > believe acquired its color before it was taken
> out
> > of the ground, by whatever means it was
> imparted.
> >
> > If I don't use the qualifier "natural", it is
> > because I have reason to believe was given its
> > color by some means after it was mined. Of
> course
> > the great majority of citrine out there is not
> > natural (in color).
>
> Fair enough :-)
>
> I would only add that the cause of colouration may
> be the same, whether of geological or some
> man-made origin.
Yes of course.
14th Jan 2013 22:05 UTCOwen Lewis
-------------------------------------------------------
> Owen Lewis (2) Wrote:
> --------------------------------------------------
> -----
> > Ken Ceglady Wrote:
> >
> --------------------------------------------------
> Oranges and lemons are common names for different
> species of Citrus, and within each there are a
> number of varieties. But I nitpick.
Niipick ^2
The species is citrus. Orange and lemon are trade names (since you prefer that term) applied to varietals. These trade names have no scientific application
:)-D
> Since we are discussing the use of a gem trade
> name, not a mineral species name, then my opinion
> is just as valid as anyone elses.
> You don't have
> to agree with it. Who regulates gem trade names?
> Anyone?
There may well be no authority for the use of words beyond convention but observance of convention is essential, in the main, to preserve meaning and useful communication. The sole purpose of words is for communication.
If you choose to call oranges lemons and I wish to call oranges grapefruit but only on Mondays, Wednesdays, Saturdays, all the Saint's Days and on my wife's birthday but also to call them oranges for the rest of the time, how can we communicate meaningfully about them?
Similarly, if you and I do not follow convention in use of ruby and sapphire as (time-honoured) tradenames not known to be two varieties of gem-quality corundum, how shall we communicate well about gem quality corundum?
In short, neither you nor I can set the rules but need either to adopt the word-usage of the herd, modifying our usage as the herd changes its usage, or to pick on our own descriptive words but ones that the other of us (and the herd) can instantly and correctly associate the intended meaning. We are not - cannot - be free to decide as just we like. There must always be the implicit agreement of others in the use of words, else meaning is lost. This topic gets philosophical quite quickly; the control of vocabulary was one of the underpinnings of the Marxian adaptation of the Hegelian dialectic :-)
'Nuff said?....
14th Jan 2013 22:57 UTCRock Currier Expert
15th Jan 2013 00:44 UTCWilliam W. Besse Expert
If Mindat does not have enough definitions already for citrine we could add in US Bureau of Mines: A Dictionary of Mining, Mineral, and Related Terms:
citrine; citrine quartz. Not the true topaz of
mineralogists, but a yellow variety of quartz.
which closely resembles it in color though
not in other physical characters; it is of
much less value than true topaz. Known
under a variety of geographical names such
as, Bohemian topaz, Indian topaz, Madagascar
topaz, Madeira topaz, and Spanish
topaz. Brazilian topaz is the true mineral,
Also called quartz topaz. See also false
topaz; smoky quartz.
From Chamber’s Mineralogical Dictionary
Bill
15th Jan 2013 01:08 UTCOwen Lewis
-------------------------------------------------------
> We could take it upon ourselves to create
> definitions for citrine and other kinds of quartz
> and suggest that they be used.
Yes, we probably could. What constitutes a 'critical mass' for the modification of language conventions depends of the size of the community effected. Many if not most families develop words that only have meaning within the family or close friends.
15th Jan 2013 02:02 UTCAnonymous User
-------------------------------------------------------
> Ken Ceglady Wrote:
> --------------------------------------------------
> -----
> > Owen Lewis (2) Wrote:
> >
> --------------------------------------------------
>
> > -----
> > > Ken Ceglady Wrote:
> > >
> >
> --------------------------------------------------
>
>
> > Oranges and lemons are common names for
> different
> > species of Citrus, and within each there are a
> > number of varieties. But I nitpick.
>
> Niipick ^2
> The species is citrus. Orange and lemon are trade
> names (since you prefer that term) applied to
> varietals. These trade names have no scientific
> application
> :)-D
Citrus is a genus, not a species. If you want to talk plants, I'm happy to (I'm a botanist), but this is not the point.
>
> > Since we are discussing the use of a gem trade
> > name, not a mineral species name, then my
> opinion
> > is just as valid as anyone elses.
> > You don't have
> > to agree with it. Who regulates gem trade
> names?
> > Anyone?
>
> There may well be no authority for the use of
> words beyond convention but observance of
> convention is essential, in the main, to preserve
> meaning and useful communication. The sole purpose
> of words is for communication.
>
> If you choose to call oranges lemons and I wish to
> call oranges grapefruit but only on Mondays,
> Wednesdays, Saturdays, all the Saint's Days and on
> my wife's birthday but also to call them oranges
> for the rest of the time, how can we communicate
> meaningfully about them?
>
> Similarly, if you and I do not follow convention
> in use of ruby and sapphire as (time-honoured)
> tradenames not known to be two varieties of
> gem-quality corundum, how shall we communicate
> well about gem quality corundum?
>
> In short, neither you nor I can set the rules but
> need either to adopt the word-usage of the herd,
> modifying our usage as the herd changes its usage,
> or to pick on our own descriptive words but ones
> that the other of us (and the herd) can instantly
> and correctly associate the intended meaning. We
> are not - cannot - be free to decide as just we
> like. There must always be the implicit agreement
> of others in the use of words, else meaning is
> lost. This topic gets philosophical quite quickly;
> the control of vocabulary was one of the
> underpinnings of the Marxian adaptation of the
> Hegelian dialectic :-)
>
> 'Nuff said?....
If I were saying that I choose to call yellow topaz "citrine", or yellow scapolite "citrine", etc., then feel free to disparage my opinion. I'm a little confused at the strength of your reaction when I simply said that citrine is yellow quartz. Is it quartz? Is it yellow?
Scientifically - based on accepted names - I cannot call an orange a lemon. Based on the mineralogically accepted name of quartz and the appearance of the color yellow, I can call it citrine. If there is a scientific standard that says it can only be called citrine if it contains X, Y, or Z, or has some other measureable property, please enlighten me.
15th Jan 2013 03:44 UTCOwen Lewis
-------------------------------------------------------
> I'm
> a little confused at the strength of your reaction
> when I simply said that citrine is yellow quartz.
> Is it quartz? Is it yellow?
We've been missing each other, Ken I think. Not hard to do in this sort of exchange. I was addressing what I took for a key point of yours, i.e. that you were free to coin names howsoever you chose and without regard to common (correct) usage.
As as generality, I'd be all for basing a system of varietal naming on the mineral species name with an easily observable rider, such as colour. However many choose to use the name citrine, one cannot be wrong to describe the variety as yellow quartz - because that is what citrine is. Misunderstanding could only arise in those who consider citrine to be something other than yellow quartz - and that'd be *their* error and problem.
Knowing something of the process where by many varieties of minerals (and some species themselves) come to have names with old historic origins that are not to be usefully obliterated overnight, I very much dislike the continual coining of new tradenames and using these as varietal names to promote insignificant or irrelevant differences simply for business advantage. Hence, in serious company, why not refer just to green grossular and leave 'tsavorite' 'merelani mint' ets to the shopping channel afficionados. But no need to repeat what has already been set out here.
15th Jan 2013 13:09 UTCAnonymous User
Understood.
24th Feb 2013 13:12 UTCRolf Luetcke Expert
24th Feb 2013 16:41 UTCDuncan Miller
24th Feb 2013 18:22 UTCJason Evans
My own photo had a message that it was iron stained quartz and whilst I agree that some of the crystals are iron stained, because they are a more brownish red colour and the faces are dull and opaque, but there are also many sparking transparent crystals with a more yellow colour and I still have it in my collection labelled as citrine.
Just out of interest I would be interested to see if anyone also agrees it is citrine and also i have another crystal which i would like to know if it is just iron stained quartz or if i can call it citrine.
http://i255.photobucket.com/albums/hh160/AstroGeo/Minerals/Citrineorironstainedquartz1024x767_zps464bea21.jpg
http://i255.photobucket.com/albums/hh160/AstroGeo/Minerals/isthisCitrine1024x768_zps8c8d911f.jpg
25th Feb 2013 06:59 UTCDuncan Miller
25th Feb 2013 11:43 UTCJason Evans
25th Feb 2013 12:52 UTCBob Harman
17th Sep 2013 09:29 UTCJennifer Shipley
-------------------------------------------------------
>...Bear in mind that Citrine formed
> in the ground results also from heat treatment...
>
>The presence of Ferric Iron(Fe+++) is necessary to turn Rock Crystal yellow.
>
Owen,
Aluminum built into the crystal lattice that is exposed to gamma rays also makes quartz yellow, and when you expose this material to heat, the yellow actually fades.
One could say that there are three types of citrine, if you include heat-treated amethyst: 1. HTA, 2. Naturally-heated iron citrine and 3. Aluminum citrine. Yellow color in itself does not make citrine, because Eisenkiesel/Ferruginous Quartz can be yellow (colored by inclusions of iron compounds on the inside) and tangerine quartz can be yellow from iron oxide on the outside (iron staining.)
In my opinion, the only true citrines are the natural ones not colored by inclusion, which would be the naturally-heated iron bearing quartz and aluminum quartz. Smoky quartz is irradiated aluminum quartz as well, but it also contains lithium, which lessons the yellow coloring. The more lithium, the less yellow until the ratio is high enough for there to be no yellow, according to one study (L. Jung: High Purity Natural Quartz For Industrial Use, Quartz Technology, Inc., Liberty Corner, New Jersey, 1992.) This whole Li:Al ratio thing also accounts for all the smoky citrines (aluminum smoky citrines, that is.)
For those interested, here are some tips for determining whether you've got a real aluminum citrine or heat-treated amethyst:
Aluminum citrine grows in shapes like clear quartz and smoky quartz and is rarely in clusters, and these clusters tend to look a lot different from amethyst geodes. Amethyst and heat-treated amethyst is most commonly seen in geode forms or in crystals that are broken from a geode, though there have been many excellent multi-terminated and skeletal amethysts flooding the market recently. If a citrine has long, parallel or gradually tapering sides, then it is most-likely not heat-treated amethyst since amethyst rarely grows in that form.
Amethyst crystals broken from geodes (including those heat-treated) are clear-white at base and get darker/more saturated toward the tip. Aluminum citrine often has phantoms which cause it to be darker in the center and lighter at the termination...opposite of an amethyst.
Also, aluminum citrine tends to range from lemon yellow to smoky yellow to olive green. The hue generally teeters on the green side of yellow's mid spectrum. Heat-treated amethyst is bright goldenrod, yellow-orange, orange, amber, brown...always yellowish hues that lie on the orange side of yellow's midline...that means anywhere from an ever-so-slight, almost imperceptible hint of gold to intensely orangish brown. If it has an olive-green tint, it is not heat-treated amethyst.
Unfortunately, I do not know how to tell if a citrine or smoky quartz has been artificially irradiated, but the presence of phantoms or cloud-like variations in the saturation of color has been suggested to indicate the crystal was not irradiated by man, but since there are plenty of natural smokies and citrines that are colored consistently throughout, you can't use that to determine if some thing is fake.
Another thing I want to mention, some ferruginous quartz looks a lot like heat-treated amethyst. I'm thinking particularly of the ones included with goethite or limonite. Both as inclusions color a crystal yellow. It's difficult to tell what exactly Jason Evan's has in his first photo (the cluster) because I can't get in close enough. It could be ferruginous quartz with geothite and hematite. Those yellow crystals look really shiny. Iron staining dulls the surface a lot in the more saturated areas and you can see it on the surface . He will have to determine if the color is a coating underneath the surface - crystals coated with geothite (yellow) and hematite (red) then sealed with a layer of clear quartz. You can probably tell with a jeweler's loupe. I have some ferruginy clusters that have hematite both underneath the surface and on the surface...and some clusters that have some sections of clear, speckled phantoms with other solidly coated phantoms...there is a lot of variation. Also, ferruginous quartz is translucent to opaque, not a tinted transparent like amethyst - ferruginous's color is an internal coating which blocks light, not a tint.
Here is an example of aluminum citrine from Sichuan, China (like the Nambian and Congo citrines):
I've got an album of aluminum citrines at:
http://s46.photobucket.com/user/jennifershipley/library/Citrines?sort=4&page=1 Only snapshots, but you can see how the color changes depending on angle, light source and background.
Here is a close-up of a very dark smoky (morion) aluminum citrine with some great phantoms:
And here is Eisenkiesel, Ferruginous Quartz or golden healer quartz:
- It is not citrine. It's color is created by inclusions of iron compounds and various other minerals.
The next one has actinolite needles:
http://i46.photobucket.com/albums/f127/jennifershipley/Jewelry%20Samples/goldenhealerrutilated1x1.jpg
and the third with finer yellowish brown needles, probably still actinolite:
https://img1.etsystatic.com/013/0/5374252/il_fullxfull.456576153_noou.jpg?ref=l2
24th Sep 2013 22:34 UTCOwen Lewis
That said, I don't fully agree with you. The truth is that at the root of this discussion is not what anything *is* but the meaning assigned to words. Words are a main means by which we differentiate conveniently between one thing and another. It matters not the scale of difference, only the importance of registering, fpr a clear understanding, some shade of difference in meaning.
We agree, I hope, that:
- Some amethyst turns yellow (becomes citrine) if heated - it matters not at all what the cause of the heating is. Heating to 400-450 deg C produces a light yellow citrine. If heated to 500-550 deg C, this darkens to produce a deep yellow or orange citrine. Should it be heated to 600+ deg C, the colour centre that is the cause of colour in citrine is destroyed and the quartz becomes milky to colourless, That is to say that the material only forms citrine if heated to within a quite closely defined temperature band. Geological or anthropogenic origin of the heating has no effect in this; it is not possible after the event to differentiate the one cause from the other.
- For citrine to form from amethyst requires not only heat but that the amethyst must, in the first place, have its colour centre determined by the presence of Fe+++ in the crystal lattice. Amethyst may also form if iron is bonded into the lattice in the form Fe++ but, where this is the case, then heating the amethyst first turns such amethyst colourless (at 350-400 deg C) and eventually to green at 400-500 deg C, this also changing to milky/colourless on further heating to 600+ deg C
The authority for this comes from widely documented research carried out more then 30 years ago and there is no scientific counter-case that I know of that has been authoritatively presented. The requirements for citrine are
1. A particular chemical mix and crystal structure.
2. An alteration in the colour centre due to the absorption of energy. Because there is no change to the crystal structure this is a study not pursued by all mineralogists
The term 'citrine' in science is restricted (see Webster (gemmology) and Frondel (mineralogy)) to yellow quartz formed by the above process. I.e. all citrine results from the heating of amethyst quartz containing contains Fe+++ and the limited heating of such amethyst. AIUI this defines the meaning and proper use of the term of citrine in scientific discussion.
So, what of your 'aluminium citrine'? Much/most natural rock crystal has some aluminium oxide bonded in. If this is irradiated (again, it makes *no* difference if the irradiation is natural or anthropogenic) the colourless rock crystal changes colour to become smoky quartz. If smoky quartz is heated modestly (140-180 deg C is typical) smoky quartz will become greenish-yellow. This is most frequently not a particularly desirable colouration and retains elements of smokiness (as your pics show). This colour change also results from the formation of a colour centre but a different one from that which forms citrine. Accordingly it does not help clarity in meaning to call such material 'citrine' also. It's not quite the same stuff and is differently caused. Where this greenish-yellow product is of pleasing quality and without smokiness, it is called 'lemon quartz' by some - or, if less desirable (definite in colouration) is just 'greenish-yellow quartz'.
But, of course, nature runs a dirty workshop and, therefore, quartz is commonly produced *by nature* in which both sets of characteristics are mixed. Thus, in reality, subjective judgements are made on a qualitative basis.
As you point out, eisenkiesel is something completely different, in which there is/are no colour centre(s) within the quartz crystal lattice itself but, rather, there are minute particles of yellowish-coloured iron oxide trapped within the quartz and, as you point out again, those can be particles of one or more iron compounds and are not bonded in the lattice. This make the colouration of th quartz of the nature of a dye (one substance lending its colour to another of much greater volume which remains without colour of its own). So not citrine; eisenkiesel.
25th Sep 2013 00:01 UTCAlfredo Petrov Manager
Quartz that is intrinsically yellow ("true citrine") can be easily distinguished from quartz colored yellow by submicroscopic iron oxides with a simple dichroscope - the yellow in the true citrine will be dichroic.
23rd Nov 2013 16:02 UTCCharles Rothera
My friend, a local shop owner, immediately declared it heated.
I have read almost all the posts concerning this terminology (and don't know the origin of this piece, thus the low price paid) and am left just as confused.
Regardless of the term, please look closely at the purplish, roundish "splotches. They do not break the surface of the surface planes and do show from one view, that what is visible extends into the crystal about 2mm and appears as the bottom of a white bowl. Also there are many locations where they are concentric and some are fibrous. Please offer any comments that may be helpful. Thanks
24th Nov 2013 10:39 UTCRock Currier Expert
24th Nov 2013 14:15 UTCHerman Du Plessis
Herman
24th Nov 2013 16:10 UTCDmitriy Belakovskiy
I can see that on the label for the crystal on the right side it is printed Perekatnoe (which is near Aldan in Yakutia) and on next line is Polar Ural. The specimen looks like heated citrine from polar Ural and doeas not looks like the specimens from Yakutiya.
So most likelty Perekatnoe is given wrong not the Polar Urals.
All the best, Dmitriy Belakovskiy
26th Nov 2013 12:59 UTCRock Currier Expert
30th Nov 2013 18:25 UTCStephanie Martin
Thank you for the locality information. Are you saying that most of the citrines from Perekatnoe were heated? Were there natural citrines from there? There a number of photos in the gallery, wondering if those are all heated too.
Thanks for any info.
regards,
stephanie :-)
30th Nov 2013 18:31 UTCStephanie Martin
Your spots look like iron oxides of some type, hematite or such. Hard to tell from the photo if it is heated or just natural iron stained (which is not technically citrine), but I would lean toward heated. There are a lot of heated citrines with specs of iron oxide inclusions that come out of Brazil.
regards,
stephanie :-)
17th Jan 2014 23:06 UTCMichael Otto
18th Jan 2014 00:05 UTCOwen Lewis
The short-form answers are that there are two varieties of transparent yellow quartz. One is a derivative of smoky quartz and the other is a derivative of some amethyst..
In turn smoky quartz is formed by the irradiation of colourless quartz (rock crystal) in which a small percentage of the Si atoms in the lattice have been replaced by Al. Amethyst results from the formation of a colour centre in quartz caused by the presence of either some Fe++ or Fe+++ ions in the crystal lattice.
If amethyst containing Fe+++ is heated it changes into citrine which can be a very attractive colour. If smoky quartz is lightly heated it turns a greenish yellow colour that is is usual easily differentiated from the colour range of citrine and is considered less attractive. This is sometimes called lemon quartz or just yellow quartz. So, slightly different colors and with different causes.
Over-heating will eventually cause both smoky quartz and amethyst (either type) to revert to a colourless state. that may be a little milky. Irradiating either lemon quartz or citrine will cause a reversion to smoky quartz or amethyst respectively.
18th Jan 2014 00:21 UTCBob Harman
18th Jan 2014 01:00 UTCOwen Lewis
18th Jan 2014 13:01 UTCMichael Otto
18th Jan 2014 14:45 UTCSpencer Ivan Mather
Spencer
18th Jan 2014 14:49 UTCOwen Lewis
-------------------------------------------------------
> ...amethyst
> is heated to produce what is sold as citrine.
>
Not quite.
1. Fe+++ amethyst when heated (400-450 deg C) gives pale citrine which darkens if the heating progresses to 500-550 deg C. Heated above 600 deg C the citrine reverts to colourless/milky quartz. This is the only true citrine. Much other stuff is sometimes sold under the same name but which is not citrine.
2. Both heating and irradiation occur as either geological or man-made processes. It may be impossible to tell whether the cause of such treatment of quartz was geological or not. The processes and their effects are identical. The only difference is the time scale over which they are applied.
Your photos seem to have a colour-cast in them (taken by tungsten lighting?). From the fact that you extracted them from the same pocket as contained smokys in another part of the pocket I'd say it was a fair guess that your specimens are smokys in incomplete conversion to lemon quartz. The smoky to lemon quartz conversion occurs at temperatures in the range of a domestic oven. So, with a good digital oven thermometer as your only equipment, you can easily test this conjecture by extending the heating of a specimen in your own kitchen.
Take it gently if you do this as the colour change with temperature rise is not uniform, being affected by the exact molecular composition of the quartz. Nassau K. gives the following information:
- Conversion from smoky to greenish-yellow can occur in the temperature range 140 - 280 deg C *BUT* conversion from greenish yellow to colourless can also occur in the entirely overlapping temp range 140 - 380 deg C.
So your outcome of any heating in the 140-280 deg C range is uncertain - so proceed in small increments of temperature rise and examine the specimen for colour change between each incremental rise.
My *guess* would be that with partial colour change already having occurred, you should be unlikely to see further change in one of your specimens below something like 200 deg C, but who knows?
If you make this experiment, do please come back and let us know the results.
All or which is a long-winded way of saying, no, I don't think you have a find of citrine on this occasion.
18th Jan 2014 16:59 UTCMichael Otto
21st Mar 2014 12:13 UTCTom Shango
http://i133.photobucket.com/albums/q61/privlaka/2014-03-21125157.jpg
All the best!
24th Mar 2014 23:37 UTCRock Currier Expert
20th Apr 2014 16:52 UTCdoorguy22
21st Apr 2014 01:09 UTCRock Currier Expert
It is difficult for knowledgeable people here to give your post any kind of meaningful reply without seeing a picture of what it is your are talking about. The term Lithium quartz which is not a scientific term, can mean be many things. The fact that it smelled indicates that is was some sort of porous material that had been soaked in some sort of volatile organic chemical whose smell increased as you heated it. Did you use warm or hot water to wash it? It is very common for unscrupulous sellers to do anything they can to make their goods look better, at least long enough to get them sold. In its mildest form, and perhaps the most common treatment is for almost all commercially sold tumbled stones, as a last process before sale, to be soaked in hot Paraffin. When the stones are removed from the Paraffin, the excess is rubbed off, commonly in saw dust, and as the stones cool, the excess is usually absorbed into the stone by contraction, filling in cracks voids in the stone, making the stone have a more intense color. Often, especially in the case of "turquoise" and "jade", all manner of fillers, dies and chemicals are used to treat them to make them look better. The subject of treated natural materials is a vast one and seems limited only to ones imagination.
8th Jan 2015 19:03 UTCDan Costian
I would call it clear peach quartz. I cannot range it as citrine, smoky or rose. I suspect the pale yellow with accents of pink might be due to iron.
How would you call it?
8th Jan 2015 19:17 UTCReiner Mielke Expert
8th Jan 2015 21:41 UTCBob Harman
8th Jan 2015 22:12 UTCDan Costian
29th Jan 2015 07:11 UTCH. Claire Scheepers
29th Jan 2015 09:11 UTCBen Grguric Expert
29th Jan 2015 13:44 UTCOwen Melfyn Lewis
21st Mar 2015 06:34 UTCtalib
Dear, i hape that at you all ok my dear i have this same golden topaz which i had sent you some image.
21st Mar 2015 12:30 UTCJosé Zendrera 🌟 Manager
Regards.
21st Mar 2015 17:52 UTCOwen Melfyn Lewis
Can't be sure from the image that what you have is citrine - but it is quartz. Natural citrine is relatively rare. Most in the market is either synthetic (I don't think your specimen is synthetic) or is the result of heat treatment of some natural amethyst (more common).
19th Apr 2016 22:03 UTCarpeey
19th Apr 2016 22:14 UTCAmir C. Akhavan Expert
They look cut and polished. Probably artificially irradiated and/or heated material from Brazil.
If you see smoky phantoms (often suspicuously off-axis) then probably not heated, but "only" irradiated.
Someone who deals with this material in Brazil would probably know, unfortunately Rock Currier is gone :-(
Value - no idea.
20th Apr 2016 07:45 UTCarpeey
20th Apr 2016 10:32 UTCAmir C. Akhavan Expert
20th Apr 2016 14:11 UTCOwen Melfyn Lewis
20th Apr 2016 15:00 UTCarpeey
It does make sense though! (tu)
20th Apr 2016 15:38 UTCBob Harman
20th Apr 2016 16:48 UTCOwen Melfyn Lewis
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> Thank you for your answers people looks like I
> have found a very helpful forum with you.Dying is
> interesting indeed.How do they do that?I read
> about irraditation and heating but dying?
> It does make sense though! (tu)
It's a favourite trick in the cheap jewellery market - especially with quartz . The crystal or cut gem shape is heated and then dropped into an aqueous solution of some coloured dye. This produces cracks in the crystal and the coloured dye is drawn into them , the water then evaporating leaving the colour behind.
If (as with the items in question?) there are already fractures in the crystal it can be sufficient to heat only gently (200 deg C or so). The crystal will not crack further but the dye will be drawn into the pre-existing cracks.
Poor quality jadeite is also frequently dyed to improve its colour and saleability. In jadeite, emerald and more, the dyeing process is most frequently accompanied by a polymer resin filler, so that the cracks are stopped up and polished over. Quartz is probably too cheap a material to fuss over :-)
Black onyx is invariably dyed, drawing first a sugar solution into the naturally pale porous material, letting it dry out and then drawing concentrated sulphuric acid into the stone to change the sugar to pure black carbon. This particular trick has been known for a couple of thousand years or so ;-)
20th Apr 2016 16:50 UTCarpeey
-------------------------------------------------------
> HI ARPEEY, Thanks for your postings! Just
> a few words about English. DYING vs DYEING.
> Your use of the word DYING might get you more than
> you bargained for as it has to do with ceasing to
> live.....such as "my father is dying". DYEING,
> on the other hand, has to do with adding colors to
> an object like a piece of clothing or a rock....."
> I am dyeing the quartz yellow to make it citrine".
> CHEERS......BOB
Thank you Sir BOB! Its definitely not my fault Owen started it not me~:)-D and it got me ..so I searched ...and again searched a little more but as I could only get hits related to death I had to ask..Otherwise I could have figured..Now you BOB just put everything in order.Especially my order..which will not happen.I am looking for a true citrine not some manmade tortured crystals.I want Golden real citrine created by Mother Earth as is ..This dyEing thing is unbelievable who would have thought about THAT!(not me)
how about this one?Is this real everyone agrees?
20th Apr 2016 18:31 UTCarpeey
6th May 2016 14:56 UTCRicardo Fabbrin Expert
7th May 2016 01:24 UTCAlfredo Petrov Manager
7th May 2016 14:25 UTCOwen Melfyn Lewis
-------------------------------------------------------
> The bigger one is around 1.5 kg.I know there is
> little chance is citrine but looks so much like it
> is ..To me at least..
>
Unnamed 2.jpg Bottom left of the group and possibly centre-bottom-right? Can't say these are but can't rule it our without a better examination. Some of the others shown are clearly not dyed but also do not look 'right' to me. Never buy off a photo (especially low-grade photo) without an absolute right to return for cash back - never 'house credit' in lieu of cash back.
18th Oct 2018 14:34 UTCAzalea Lee 🌟
I understand that it has to do with the oxidation state of iron impurities. But what is the influence of heat to the degree of change in color? And what is happening that causes the heat treatment to permanently change the amethyst's color?
18th Oct 2018 17:14 UTCDoug Daniels
18th Oct 2018 17:56 UTCOwen Lewis
I don't think that a 'lay person' is going to find a satisfactory answer to to such a narrowly focused question. Every answer will simply produce more questions. Rather, bite on the bullet and set about understanding the several causes of colour (Nassau reasoned that there are 15). For yor focus, in particular you need an understanding of colour caused by transition metals in a ligand field and also e-m radiation absorption at points in the optical band by colour centres. D'you see what I mean about answers leading to more questions? AFAIK, there is only one book in English that deals with this thoroughly and that really must be the primer for those, like thee and me, seeking to understand these issues that are grounded in atomic physics and in the behaviour of orbital electrons in particular. If you have a good basic education in science, I strongly recommend you get a copy of Kurt Nassau's 'The Physics and Chemistry of Color' and read and keep re-reading at least the chapters dealing with fundamentals and colouration in minerals until sufficient of this great book sink in. Anyone can try to bluff their way but I sense that you really do want to understand. Good for you! It's a fascinating little niche study.
Another good book (also by Nassau) is 'Gemstone Enhancement'. This does not explain the fundamental principles but is rather a 'cook-book', setting out clearly what colour and transparency changes can be wrought in minerals important in the gem trade , giving what the changes are, the necessary conditions for the change, reversibility or otherwise. The several colour variations that can be produced in quartz (always essentially a colourless material) are fully detailed.
18th Oct 2018 18:25 UTCKevin Conroy Manager
19th Oct 2018 00:17 UTCBenjamin Oelkers
In amethyst, the violet colour is caused by iron in the unusual oxidation state +IV, surrounded by four oxygen atoms. The iron was incorporated into the quartz crystal as it grew, and the energetically unfavourable change from Fe3+ to Fe4+ was caused by gamma radiation. Where the electron goes does not bother us too much here. The colour is relatively stable because everything is "frozen in place" at ambient temperatures.
When the amethyst is heated to a yellow to orange quartz, energy is again available to the "unhappy" Fe4+ ions, and they become a little bit mobile. Because of that, they can a) grab an electron from "somewhere" (similar to above) and b) get together to form very small particles of some kind of iron oxide. And just like any old iron staining, that can be seen as a yellow to orange colour.
After the heating process, everything is again "frozen in place", and the new colour is stable.
19th Oct 2018 06:32 UTCKevin Hean
Is it true that if you irradiate Citrine the colour will return to that of Amethyst ?
19th Oct 2018 10:01 UTCBenjamin Oelkers
I am no expert on this matter, but I do not think that would work, at least not reliably. The reason for my guess is that the heated amethyst gets its yellow colour from finely dispersed iron oxide minerals, which means that upon heating some sort of aggregation of the iron takes place inside the crystal. And while it should be possible to reform the Fe4+ colour centers using radiation, I do not think the aggregation of iron will be reversible.
Real citrine, on the other hand, could behave quite differently. According to the citrine page here on mindat, reversible colour change yellow->colourless->yellow is possible with authentic citrine upon heating (loss of colour) and subsequent irradiation (re-formation of colour centers).
19th Oct 2018 13:36 UTCKevin Hean
Thanks for the information, my interest certainly has been piqued.
26th Oct 2018 00:47 UTCcascaillou
26th Oct 2018 06:25 UTCKevin Hean
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