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Identity HelpDifferentiating Phenakite from Topaz

15th Oct 2014 23:35 UTCVitya

In the process of cataloging and going through my collection I found some specimens from Volodarsk-Volynskii. These were obtained in the very early 2000's and I have identified a few Topaz based on locality pictures. However I have some smaller specimens from there that I am having difficulty distinguishing between Phenakite and Topaz. The Phenakite from that locality is shown in various specimens as being somewhat cloudy and also being more translucent and semi-transparent. I remember when I obtained my specimens from local dealers at that time that I remember obtaining a few Phenakite specimens. However I am wondering what would be the best way to differentiate between colorless topaz and Phenakite as they are somewhat similar in appearance from the locality and hardness . Unfortunately I do not have any pictures at the moment.

I appreciate any help or suggestions on this in advance.

16th Oct 2014 10:00 UTCErik Vercammen Expert

I don't know (the specimens from) this locality, but there is a diffrence in crystal system, topaz being orthorombic and phenakite being trigonal. This mineral has a good cleavage // with the c-axis, while topaz has aperfect cleavage, that sometimes can be seen in crystals.

16th Oct 2014 13:56 UTCMarc Maes

Phenakite gives a diamond result on a diamond tester (thermal conductivity type), topaz doesn't.

17th Oct 2014 02:13 UTCRock Currier Expert

Now that's interesting! Do you know anywhere that has been written up?

17th Oct 2014 04:25 UTCDoug Daniels

I agree with Rock - is there a reference? Doesn't seem likely based on physics, and then would probably be very dependent on where on the crystal it was tested (just thinking out loud).

17th Oct 2014 10:50 UTCMarc Maes

I've done the test with a duotester of presidium on a phenakite crystal. There was an article of Gemlab http://www.yumpu.com/en/phenakite

17th Oct 2014 16:32 UTCOwen Melfyn Lewis

An SG test would be categoric in a phenakite/topaz shoot-off. Others too, including the isogyre pattern.

10th Jan 2015 18:20 UTCPatrick Darling

Guys, you all seem quite knowledgeable on this topic and I happen to have the same issue over a uniquely formed piece I obtained from Pakistan from a mine that apparently has both topaz and phenakite. I paid a premium for phenakite but later was told it could be topaz. I don't yet understand the difference of orthorombic and trigonal crystal systems enough to know for sure. It just has a very unique crustal shape for either, so your wisdom would be much appreciated.

I've attached several photos of the piece. Can any of you chime in and confirm for sure which it is? Thank you kindly.

11th Jan 2015 13:42 UTCReiner Mielke Expert

Hello Patrick,

I hate to tell you this but it looks like quartz to me, but I could be wrong. Can you scratch it with a piece of topaz? If so then you have quartz.

11th Jan 2015 13:51 UTCSpencer Ivan Mather

I would also say that that looks a lot like quartz to me..

11th Jan 2015 14:18 UTCAlfredo Petrov Manager

I agree with Reiner and Spencer. Looks like a doubly terminated quartz.

13th Jan 2015 04:06 UTCPatrick Darling

Well gents - I tried the topaz scratch (thanks for the idea) and will say that yes, with some hard scratching with a pointed topaz, I was able to scratch it enough to see the scratch with a loupe, but from what I can find, topaz has a hardness of 8 while phenakite is 7.5 - 8, no?... so it that an end-all test? I'm surely willing to concede if so, I just want to make sure before I go demanding my money back. Any other tests I can do at home?

13th Jan 2015 16:25 UTCD. Peck

Patrick, Look at the terminations of the crystals. I am particularly looking at the upper most one in the third photo. Does the termination have three major faces, each at 120^o to the others? If so, it is trigonal and could be phenakite (or quartz). Topaz is usually a bit blocky and shows four major faces on the termination.

Can you see any incipient cracks (cleavage planes) in the crystals? Topaz has one perfect cleavage plane, and it is perpendicular to the "prism" of the crystal. Phenakite has three distinct (not as good as perfect) cleavage planes and they are parallel to the prism of the crystal.

If there is a broken crystal, anywhere on your specimen, that you can sacrifice, a specific gravity ought to be definitive.

13th Jan 2015 16:44 UTCReiner Mielke Expert

Hello Patrick,

You are right about the hardness, I should have said if you can easily scratch it but "easily" is a relative term and as such the test is inconclusive. You would have to try scratching a known phenacite and then compare the results. However, D.Pecks suggestions are more definitive particularly the cleavage as quartz almost never exhibits a cleavage.

15th Jan 2015 14:14 UTCHarald Schillhammer Expert

Actually, I have as yet to see a "real" phenakite from Pakistan with my own eyes. All I have seen so far turned out as topaz, quartz or scheelite. Even now here are several on ebay, and all of them are topaz.

18th Jan 2015 03:50 UTCPatrick Darling

Thank you all again guys - I think after what you have said, it's ~99.9% likely to be quartz. I'm finding the same thing Harry said too - I'm doubting there are phenakites at all coming out of Pakistan. I'm told they're selling it locally in the markets as phenakite and being 'the deciever' stone, many people don't know the difference and so they sell them that way. I'm sure there are those too who do know and sell them anyway. Thanks again for your input and wisdom to help me know what I have here. Quite a cool little double-terminated quartz though actually.

29th Jan 2015 22:37 UTCScott Rider

I too have noticed that some people don't seem to know the differences. eBay sellers have been listing some Phenacite as Phenacite var. Topaz. So I don't know if they are being deceitful or if they are ignorant on the subject. I personally think they are ignorant about the differences, as some seem to think Phenacite is a variety of Topaz, which is a little odd to be honest.. But then there are some that just sell fragments of Quartz and say its phenacite, especially some Brazillian dealers (on eBay for the most part), and quite frankly those people are liars.

My friend from Pakistan, whom has mined and sold Topaz for years has never seen actual phenacite from his homeland, except for quartz being sold as phenacite. He actually got in a big long argument with an eBay seller who was claiming to sell huge phenacite specimens, in the hundreds of grams (up to 18cm), which were actually heavily etched, beautiful Quartz specimens... They were quite obvious from the images I've seen that they are clearly quartz. He tried to call that dealer out about how that dealer was selling things that weren't right, like selling iradiated/heated specimens as naturally colored stones, enhancing color on the auction listings and selling Quartz as Phenacite, but nothing has changed. Since this is an unregulated sector, only the buyer can prevent themselves from being ripped off...

Anyway, I've taken chances with a few of those sellers and have received quite a good suite of Pakistani/Afghani minerals, but the ones selling quartz as phenacites, I just say stay away from them. Buyers beware...

30th Jan 2015 02:57 UTCPatrick Darling

I could not agree more on all counts, and I agree I think there is a good chance these sellers are consciously deceiving. One look at the color of their aquamarines, either color enhanced or radiated (yet show treatment as 'natural') and its all too clear. There's a lot of deception going on.

Thanks everyone for chiming in on this. Really helps to have input from you guys with longtime experience.

30th Jan 2015 13:08 UTCOwen Melfyn Lewis

Scott, Patrick,

I'm interested.

- How can you tell that a specimen has been either irradiated or moderately heated by man? Especially from a photograph.

- Why would one irradiate an aquamarine and what would be the effect if one did?

- SG and birefringence are certain separators of quartz and phenacite - so why is there any argument?

30th Jan 2015 14:50 UTCReiner Mielke Expert

"- SG and birefringence are certain separators of quartz and phenacite - so why is there any argument?" None unless it is attached to some matrix.

30th Jan 2015 15:46 UTCOwen Melfyn Lewis

Quite so for SG testing - so save it for clean specimens only. Should still be able to see the difference in birefringence though. But not perhaps from a photograph.

Birefringence alone won't tell one what has but it is but it's good enough, stand-alone, to know that one is not looking at quartz when that one is looking at a birefringence almost twice that of quartz. lt's very easy and precise if the stone is cut and polished and one has a TIR refractometer. However, with good transparency in the crystal and just a little experience of observing double refraction in crystals, a nearly x2 difference is observable - though in small pieces, a microscope may be necessary (certainly is for my old eyes).

I once bought by mineral auction (specialist - not e-Bay) what was described and looked like a nice, clean. Brazilian phenakite specimen but without terminations. On arrival it turned out to be petalite :-) I kept it anyway and later had it cut into two flawless jewels.

30th Jan 2015 17:53 UTCScott Rider

To answer the question in regards to the color, and whether it was artificially produced is a difficult one. The only thing I can think of is that you can reference the crystal to known images in this website's database, among others, or to post images at the forum and use the advice from the experts here. I do not claim to be an expert, but I have learned a LOT from this website and the people here. The advice here is genuine and usually candid and I feel very comfortable taking advice from the people here.

To answer why people alter the color is mainly due to money. The stronger the blue in aqua, the more money it is worth, in theory. However, with all the fraudulent items floating in the mineral shows and online, it makes it very difficult to know when something has been altered by man. So I fall back to my original advice, ask before buying, if at all possible.

I know that is next to impossible at mineral shows, so the other advice I've taken from others here is to use your best judgment, if a crystal has a very strong color, there is a chance it could be altered... Not always, but a lot of the strongly colored tourmaline from Afghanistan are apparently heated/irradiated. The smoky quartz from there is the same. For example, the smoky quartz from Colorado are genuinely very dark in color, but they resemble the dark smoky from Pakistan that have been in the market for a while, which are more than likely irradiated. I've mined Smoky here in Colorado and I can tell you they are that dark in color out of the ground. I can't say for sure about Pakistan specimens, but the consensus here at Mindat is that they are not naturally that dark (ie. morion).

30th Jan 2015 22:16 UTCOwen Melfyn Lewis

Scott Rider Wrote:

-------------------------------------------------------

> To answer the question in regards to the color,

> and whether it was artificially produced is a

> difficult one. The only thing I can think of is

> that you can reference the crystal to known images

> in this website's database, among others, or to

> post images at the forum and use the advice from

> the experts here.

The problem, surely, is that you are looking at web images. The appearance of these depends on your monitor, the lighting used to make the image, the camera settings - and, of course, the specimen itself.

On the colouration of aquamarine, I think there are three benchmark works of reference:

- John Sinkansas's 'Emerald and Other Beryls'. This large and now out of print work is (expensively) still available second-hand through the likes of Amazon - or for free through a public lending library.

- Dr K. Nassau; 'The Physics and Chemistry of Color'.

- 'Gemstone Enhancement' - Nassau again.

The colouration of aquamarine is relatively complex and due to Fe3+ and Fe2+ ions being present in the beryl molecule: Fe3+ in partial substitution for Al and Fe2+, interstitially in channels in the cyclosilicate framework. If the Fe3 alone is present, the colour is yellow and one has 'heliodor'. If both Fe ions are present one has natural aquamarine, which is sea-green. If such crystals (the most common form) are moderately heated, the Fe3+ is rendered colourless (think goshenite) and then the crystal is coloured by the Fe2+ alone which gives a blue colour. Rarely, Fe2+ only is present in Beryl and aquamarine is blue as it is mined from the earth.

Sinkansas makes the point that blue as a colour of aquamarine was virtually unknown until the 20th century though by the 1980's it was the only colour of aquamarine to be found in the gem market (present-day market preference). Natural or treated blue aquamarine can be found in anything from a blue so pale it can only be seen with a pure white reflector placed behind the crystal to a medium-strong blue.This is determined by the level of Fe2+ present.

A strong blue beryl does exist in the form of maxixe but this is rare and colour-unstable when exposed to light. It also has a completely different chromophore to the Fe of aquamarine.

To the best of my knowledge, heat treated aquamarine cannot be distinguished from the rare natural occurrence of that colour. There is some suggestion that low-heat treatments to affect the colour centres in some gems *may* be detectable by Raman spectroscopy but, AFAIK, the jury is still out on this proposition.

> ....The advice here is genuine and

> usually candid and I feel very comfortable taking

> advice from the people here.

Yes it is indeed. But you will have noticed that, as in all other talking shops, we do not always hold the same opinions when these are drawn from our own experiences This is where standard works of reference come in to their own.

> To answer why people alter the color is mainly due

> to money.

That was not the burden my question. It was, what effect will irradiation have on an aquamarine?

> The stronger the blue in aqua, the more

> money it is worth, in theory.

That may be true and is sad. Most blue aquamarine has been heat-treated. Irradiating Fe-salted beryl will not give you blue or a better blue - but irradiating maxixe will deepen its blue and (temporarily) restore the depth of blue in maxixe that has faded in sunlight.

However, with all

> the fraudulent items floating in the mineral shows

> and online, it makes it very difficult to know

> when something has been altered by man. So I fall

> back to my original advice, ask before buying, if

> at all possible.

Fraud is a strong word... but you are right in that any crystal with a chromophore that can drive colour in one direction or another with an input of energy (be it relatively high (e.g. gamma radiation) or low (heat) is always like buying a pig in a poke - unless you took it from the earth yourself. Don't be to hard on or expect too much of the rock 'n gem show stall holders. How the Bill-Hill are they to know for sure any more then you? They are too many pairs of hands between them and the miner. Most of them seem to do their best. But the imperative is to give the public what the public wants to buy.

> ....use your best judgment, if a crystal

> has a very strong color, there is a chance it

> could be altered...

Very true. Caveat emptor. Or shrug and pay small accordingly.

> ....strongly colored tourmaline from Afghanistan are

> apparently heated/irradiated. The smoky quartz

> from there is the same. For example, the smoky

> quartz from Colorado are genuinely very dark in

> color, but they resemble the dark smoky from

> Pakistan that have been in the market for a while,

> which are more than likely irradiated. I've mined

> Smoky here in Colorado and I can tell you they are

> that dark in color out of the ground. I can't say

> for sure about Pakistan specimens, but the

> consensus here at Mindat is that they are not

> naturally that dark (ie. morion).

This cuts to the chase. *ALL* smoky quartz requires two precursors:

- That some of the Si in the crystal has been substituted by Al. This is true for most quartz.

- That such quartz has been irradiated. The irradiation may have taken place in the earth over thousands of years or it may have taken place in a 'lab' over hours. Done carefully, the result is the same. In nature, irradiation will only occur where radiation-producing rocks were once in close proximity to the quartz.

The one's to watch for are those treated over-hastily and carelessly. These show 'burned toast' where the crystal is at it thinnest - point and face meets. See that and don't walk away - run. I remember seeing flats and even sacks of such stuff on sale as Ste Marie aux Mines a couple of years back, along with a couple of other pretty obvious treatments.

14th Jul 2015 22:12 UTCJoe man

Hi, I bought a price of phenacite from Pakistan. It has a mass over volume of 3. Which is the same density as phenacite. What do you think?

14th Jul 2015 23:29 UTCWayne Corwin

Joe

Why would you suspect it's not?

15th Jul 2015 01:50 UTCJoe man

Because of the beginning of the blog about phenacite from Pakistan.. I just would like to have a better idea on what the material is. Thanks!

15th Jul 2015 13:23 UTCRudy Bolona Expert

It's ironic. The Greek word phenak means deceiver. There are some very large specimens of "phenakite" from Pakistan offered on ebay. Someone should have one analyzed to see if it's phenakite or "deceiverite" and solve the Pakistani phenakite mystery once and for all. Those dealers know that a large blob of topaz isn't worth much. They are capitalizing on phenakite's supposedly magical powers. ;-)

15th Jul 2015 15:34 UTCReiner Mielke Expert

If you want to know for sure with a minimum of hassle and expense just have a tiny ( <0.1mm) fragment analyzed with EDS. http://kaygeedeeminerals.com/sem-eds_service (assuming you have ruled out quartz).

4th Sep 2015 11:47 UTCKk raju

20th Sep 2015 21:24 UTCPatrick Darling

To the wise and experienced folks at testing minerals on this thread - can you please refer me to a lab (or a sure-fire 'home' test) where I can have numerous phenakites conclusively tested to ensure they are in fact phenakite? A 'gravity test' was suggested and I've found out how to do this, and will try it out, but I would also appreciate any suggestions on professional lab testing outlets, esp. in the Sacramento/NorCal area.

I sincerely appreciate any help.

Patrick

21st Sep 2015 00:40 UTCOwen Melfyn Lewis

Patrick,

For your location, you should consider GIA in Carlsberg, CA.

'Home' methods. IMO there is no single test that should be absolutely relied on for an ID. Rather, a range of different tests are applied, each test result reducing the range of possibilities for the mineral identity of a specimen. With some luck, filtering possibilities through such a range of tests will leave only one candidate still standing. In short, the identification is a process of elimination of candidates rather than arriving at an ID in one move. That said, with experience, this process can get pretty quick and the number of tests required reduced.

For gem stones (mainly colourless/coloured and transparent crystals) the standard instruments and tests are:

1. x10 loupe. Quick examination under a standard level of magnification.

2. Dichroscope. Identify pleochroism in colored crystals and the pleachroic colours.

3. Polariscope. Differentiate singly refractive (isotropic) specimens (glass and cubic system crystals only) from doubly refractive crystals. With clean monocrystals, differentiate between uniaxial and biaxial crystals (both anisotropic). Differentiation of quartz from all other uniaxial crystals.

4. Totally internally reflecting refractometer. Measurement of refractive index or indices. Measurement of birefringence. Determination of optic character and sign.

5. UV lamps, SW and LW. Detection of fluorescence, tenebrescence, phosphorescence.

6. Hand held/desk-mounted spectroscope. Detection of diagnostic patterns of absorption of light of different wavelengths.

7. Microscope. x10 - x40 mag minimum (to x120 is better). Equipped for use in conjunction with polariscopy and study under immersion fluid.

8. Electronic scale/balance and hydrostatic weighing kit. Accurate weighings to a minimum value of at least 0.02 g for SG determination to 2DP.

9. A range of carefully chosen light sources for working with 1 - 7 above.

10. Set of uniform profile scratch styli for Mohs values 3 - 9.

11. Neodymium magnet and test rig for testing magnetic response.

12. Per mineral, reliable tables of comparative values and value ranges for the above tests.

21st Sep 2015 16:32 UTCD. Peck

Owen, I think that is Carlsbad, California, not Carlsberg.

21st Sep 2015 17:44 UTCOwen Melfyn Lewis

Freudian slip Don. Thanks! :)-D

21st Sep 2015 19:35 UTCPatrick Darling

Thorough indeed... thank you ever-so kindly Owen!

24th Sep 2016 20:57 UTCGem and Mineral collector

The phenakite on the left is from Minas Gerais Brazil

The crystals on the right were sold as phenakite and I am unsure.

Any help would be great✳️

25th Sep 2016 10:28 UTCOwen Melfyn Lewis

SG (for reasonably clean crystals). Phenakite is uniaxial and topaz biaxial. Birefringence. Cleavage. Inclusions.

2nd Jul 2017 19:53 UTCAnton Azaro

This phenakite speicmen from Pakistan, i got just a two days ago.

2nd Jul 2017 21:04 UTCOwen Lewis

Don't think that one is topaz :-) Nice catch!

3rd Jul 2017 18:17 UTCPeter Slootweg 🌟

I do not think Antons's specimen has Phenakite crystals on it. It looks more like a groep of quartz crystals on lepidolite mica. Phenakite on lepidolite is unlikely.

3rd Jul 2017 20:11 UTCReiner Mielke Expert

I agree with Peter, looks to me like distorted quartz crystals.

3rd Jul 2017 20:22 UTCJosé Zendrera 🌟 Manager

Anton Azareo Wrote:

-------------------------------------------------------

> This phenakite speicmen from Pakistan, i got just a two days ago.

This specimen seems to be still for sale right now: Phenakite

4th Jul 2017 08:25 UTCAnton Azaro

it is phenakite, it's much heavier and harder than quartz.

4th Jul 2017 08:27 UTCAnton Azaro

by the way, most of the Pakistani phenakite coming combine with lepidolite or muscovite. Same mine which produce tourmaline and topaz as well.

4th Jul 2017 08:30 UTCAnton Azaro

22.91ct. little Phenakite

4th Jul 2017 16:19 UTCPeter Slootweg 🌟

I have yet to see a genuie phenakite from Pakistan or Afghanistan. All the so called phenakites i have seen turned out to be corroded and/ or mishappen quartz or Topaz. That's also why you do not find any pictures of phenakite from those areas on mindat, exept for a single unusual specimen with garnet.

The shape of the crystals on lepidolite does not fit phenakite but quartz. The horizontal lines on the crystals and general habit match quartz. Striations om phenakite are always vertical along the c-axis. If the crystals are harder than quartz than thats odd. The SM is hard to measure with the lepidolite attached. Phenakite does occur in pegmatites as does lepidolite but not the same kind of pegmatites, they tend to be of a different chemistry (NYF-type). To me the presence of lepidolite alone would rule out the crystals to be phenakite. Muscovite, however, is common with phenakite.

The fine crystal you posted is a true phenakite, no doubt. I guess this is a Burmese crystal, not from Pakistan or Afghanistan. As mentioned before, many Pakistani traders try to sell any colorless mishappen crystal for phenakite as they are populair among " believers" who usually can't tell the difference between quartz, topaz and phenakite, unless in well defined crystals.

4th Jul 2017 19:03 UTCAnton Azaro

The 20.91ct. crystal is Burmese phenakite, but the one on a mica is Pakistani phenakite, not quartz or topaz, or something else.

From 5 specimen I received 4 were topaz and one is truly phenakite.

4th Jul 2017 20:46 UTCWayne Corwin

Anton

Have you checked for glue?

I'm not saying it's been faked,,, but just thought I'd ask.

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