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Fakes & FraudsPrehnite vs green tourmalated quartz

29th Apr 2010 16:19 UTCRuss Nobbs

There are wonderful specimens of prehnite in the thread at http://www.mindat.org/forum.php?read,17,170881,page=1.

I'm wondering about much more mundane beads sold as Prehnite vs beads sold as green tourmalated quartz (often called green hair quartz).

Some sellers call green tourmalated quartz that does not have as many inclusions by the prehnite name. Checking mineral sites (including this one) I learned that prehnite is Ca2Al2Si3O12 (OH) a Calcium Aluminum silicate while green tourmalated quartz is quartz (SiO2) with tourmaline needle inclusions.

One seller told us "Actually when we first had it, we called it Green Tourmalated Quartz. Then we found out it should call "Prehnite". So we only use "Prehnite" now."

Is this another case of calling a better looking cheap stone by a fancier name to get a higher price?

30th Apr 2010 10:20 UTCRock Currier Expert

I think all of the Chinese prehnite beads and small lapidary items made from prehnite have come from various localities in the Kays, region of Mali. During my visit there to buy specimens I found most of the material was placed in tough plastic "burlap" bags for shipment to the cutting factories in China. Some of the material is shot through with thin black needles of some amphabole, possibly tremolite, and I suspect that is what they are trying to sell as green tourmalinated quartz. I and my buddy Dem Pohl wrote an article on the locality that has yet to appear in the Mineralogical Record.

3rd May 2010 05:41 UTCRuss Nobbs

Thanks for the reply! I'll look for the upcoming article.

Do I understand correctly that you think Chinese cut beads sold as "green tourmalated quartz" are likely to actually be Prehnite with black needles of amphabole, or tremolite?

I was guessing the other way around. It's nice to know the cutter is more accurate than my guess. Some of our Chinese cutters try really hard to get accurate names for real minerals. It's a problem when they buy the rough using a Chinese language descriptive name rather than a western mineralogical name.

4th May 2010 09:26 UTCRock Currier Expert

If you can show me a picture of exactly what you are talking about, I may be able to identify it as prehnite from Mali. It has been my experience that most Chinese will give any name to a stone if they think it will make it sell better, but that may also be true of quite a few people selling things on ebay.

6th May 2010 15:55 UTCRuss Nobbs

Here are 2 pictures of 3 strands from 2 vendors. The top strand and the 10mm round beads are from the cutter who originally called it "green tourmalated quartz" and now calls this material prehnite. Thanks for sharing your opinions on this.

7th May 2010 11:42 UTCRock Currier Expert

Yes, they are prehnite with as yet an unidentified black amphabole inclusions from the area near Benduko in the Kays region of Mali.

7th May 2010 17:20 UTCRuss Nobbs

Thanks a lot!

18th May 2010 22:55 UTCCédrick Gineste Expert

I confirm these beads are made up of Malian prehnite.

Rock did you receive my PM? Living and working in Mali, I have a good knowledge of the Kayes region and its mineralogy.

13th Mar 2011 04:37 UTCdeussala

a montreal sellers try to sell me this kind of stuff .he said that was tourmalated jade

13th Mar 2011 05:43 UTCRuss Nobbs

Ha ha!

Calling it jade based on the "fact" that anything green must be some kind of jade?

Over in the Bead collector.net forum Barbara shared this sign copied down down during a visit to the Beijing Geological Museum.

<< 'Jade' in China describes all polycrystalline and cryptocrystalline mineral aggregates and a few non-crystalline materials that are suitable for carving and making into jewellery. The caracteristics are beauty, colour, moderate hardness, tough and fine texture, and as well as nephrite and jadeite includes opal, serpentine, quartz, turquoise, lapis lazuli, malachite, dushun yu, marble, natural glass, rhodocrosite, solalite , and rhodonite.>>

No wonder there are so "many something-or-other jades".

13th Mar 2011 07:59 UTCdeussala

oh,i forget he said high quality imperial jade tourmalated .the worst liar i ever see .half of is stock was fakes minerals

17th Oct 2012 08:15 UTCeidos

I just came across this thread & perhaps most already know this by now: those are epidote inclusions in prehnite. They're commonly found in Mali prehnite, although black tourmaline needles are also possible.

17th Oct 2012 08:50 UTCeidos

Here're some nice examples:

http://www.geologicdesires.com/mineralspecimensforsalemaliafrica.htm

Scroll down to find an interesting example with tourmaline inclusions.

17th Oct 2012 17:27 UTCUwe Kolitsch Manager

Thanks, Eidos.

18th Oct 2012 03:09 UTCJim Sullivan

Good Call, Eidos-- I have several specimens of Kayes Prehnite-- All were identified to be Epidote with Prehnite. I've never seen a Tourmaline with Prehnite from there---that's not to say they don't exist, but with the prevalence of Epidote I would be inclined to believe the inclusions shown in that one piece were also Epidote--Unfortunately, his pics do not show the inclusions with any justice

18th Oct 2012 04:05 UTCStephanie Martin

I am wondering if anyone has actually tested this material? I have seen it referred to as any of epidote, tourmaline or amphibole. If I had some junk pieces I would get some tested but I'm not willing to bust up my pretty cabs and display pieces. I do know that some of the inclusions look grassy and quite green, while others look much darker almost black and vary from thin to thick blades. The inclusions don't really look like the big chunky epidotes that they grow on and around, so I even wonder about epidote, unless growing right through a crystal. I have one display piece that has really fine needles that are barely noticeable. These I suspect may be amphibole. I have my doubts about tourmaline, but unless some testing verifies that we will not know. I guess I'll try and find some rough junky pieces out there so I can sacrifice them, I've been wanting the answer to this for a long time :-) Perhaps there are all three :-S

regards,

stephanie :-)

18th Oct 2012 12:52 UTCRock Currier Expert

I have not gone to the trouble of trying to identify exactly which amphibole is present in the prehnite from Mali. It is not a simple analysis and even mineralogists with well equipped laboratories don't want to waste their time on it. It would probably cost several hundred dollars to find out exactly which amphibole it might be and even then there will soon be more, hopefully not to massive nomenclature changes for this group of minerals and it hardly seems worthwhile to go to the expense of characterizing it when the definitions of which is which may soon change again.

18th Oct 2012 13:58 UTCStephanie Martin

Rock - I'm fine with calling it amphibole, I know they won't be able to determine the exact amphibole without a lot of bother and expense. Are you saying that you had some tested and the results came back as amphibole?

My main question are the inclusions epidote, amphibole or tourmaline? Or do all three exist? I was only thinking of getting testing done to determine which it might be since no one seems to know definitively.

regards,

stephanie :-)

20th Oct 2012 10:20 UTCRock Currier Expert

Yes some of the thin black included prismatic crystals have been identified as amphibole. No tourmaline has been identified to my knowledge. Epidote crystals are a common association with the prehnite from the Kays region, but they are generally much larger and usually form in discrete crystals only rarely as inclusions inside the prehnite.

20th Oct 2012 16:39 UTCStephanie Martin

Thanks for clarifying that Rock, that was my suspicion and I feel more confident now in saying the inclusions are amphibole.

regards,

stephanie :-)

30th Jan 2013 08:30 UTCSYLLA

These gems are originated from west-Africa-Mali

Sylla

I have edited your text as it appeared to be an advertisement, and Mindat is a non-commercial site. Olav Revheim

30th Jan 2013 10:06 UTCOlav Revheim Manager

Rock, Stephanie.

If an amphibole is present with the epidote and prehnite, I would be surprised if it was not actinolite. The environment obviously an Ca-Al-Mg-Fe environment, and Al doesn't significantly enter the amphibole structure for calcic amphiboles below somewhere near 400 deg C, which is towards the high end of the prehnite stability field.

I don't know, but I guess that maybe even an EDS would be sufficient to verify actinolite in this environment ( High Ca and low Al peaks)

Olav

23rd Aug 2015 22:55 UTCBill Acland

I'm probably too late on this thread but I have only just encountered it as a result of cutting and polishing a piece of Prehnite. It has the needle like inclusions (2) which are typical of tourmaline, which I have encountered frequently in the past in other materials.

8th Sep 2015 17:38 UTCReiner Mielke Expert

EDS will tell you for sure which subgroup it belongs to and if you are lucky possibly which species.

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