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Identity HelpLuc Yen, Yenbai, Vietnam. ID of white crystals

2nd Mar 2014 23:34 UTCJuan Manuel Garriga

Hello

I have this piece from Luc Yen.

This is the typical piece with spinel crystals on marble.

The piece was in acid for show the crystals.

As you can see there red spinel crystals and other tabular crystals.

They have a high activity under UV light.

Anybody know this kind of crystals?

Thanks

3rd Mar 2014 01:11 UTCJuan Manuel Garriga

-- moved topic --

3rd Mar 2014 01:16 UTCRob Woodside 🌟 Manager

Pargasite?

3rd Mar 2014 02:45 UTCPeter Haas

Juan Manuel Garriga Wrote:

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

> The piece was in acid for show the crystals.

What acid, which concentration, and at which temperature ?

3rd Mar 2014 06:08 UTCFerdinando Giovine

pargasite for me

3rd Mar 2014 06:10 UTCJuan Manuel Garriga

Rob

I think is not pargasite.

The colour of this crystals is more white. Pargasite from yenbai have a green colour very characteristic.

I don't know if this is UV semsible.

3rd Mar 2014 06:12 UTCJuan Manuel Garriga

Peter

I have not acidified personally.

When I receive the piece it was treated, so I don't know all the details about the process.

3rd Mar 2014 07:53 UTCOlav Revheim Manager

I agree with Rob and Ferdinando that pargasite is the more likely candidate, although it is lighter than most of the pargasites. From the minerals listed from Luc Yen in mindat it is hard to see what it could be something else than an amphibole. I don't think the color is diagnostic in any way.

The normally intense green colour of the Luc Yen ( as well as for Hunza and Mogok in the same kind of environments) are due to a small substitution of Cr for Al in the C position of the amphibole, indicated as bold in the formula: Pargasite: NaCa2(Mg4Al)(Si6Al2O22)(OH)2. The light colour might indicates less Cr than common in the intense green crystals.

The light color may also indicate a higher edenite component in the amphibole, as edenite contains less Al in the C position than pargasite.

Olav

3rd Mar 2014 16:00 UTCPhil M. Belley Expert

Another option is forsterite, though it will get attacked by hydrochloric acid in any moderate concentrations, I have successfully removed some from calcite in low concentrations and cool temperatures (overnight outside) with no visible damage. I have other forsterite which did not sustain alteration from HCl due to thin retrograde diopside rims. Does the mineral have diagnostic amphibole cleavage?

3rd Mar 2014 16:15 UTCRob Woodside 🌟 Manager

Funny you should say that Phil. This AM I got an email from Dudley Blauwet which said:

"Hi Rob: I had a long day from 5 am until 11 pm working and before bed I checked mindat for a minute. You replied to a query about an unknown from Luc Yen. I had similar things analyzed and they came out as forsterite. That specimen is from the Cong Troi mine, near An Phu, about 20 km from Luc Yen via a winding road, and about half that distance as the crow flies. Interestingly there is also colorless gem quality, ( I cut some ) forsterite from the spinel locale in Tajikistan and also some have been found ( also cut into gems) in Mogok. Forsterite occurrence with spinel is not so uncommon. D"

Even so they look like amphibole xls to me:-S

3rd Mar 2014 19:51 UTCOlav Revheim Manager

Rob, Phil,

I'll try to learn to think before I write next time :-)

Thanks

Olav

3rd Mar 2014 20:26 UTCRob Woodside 🌟 Manager

Just looked at a Sar-e-Sang Forsterite (PXRD confirmed) and it has these tabular, amphibole looking, xls. So yes Forsterite!

3rd Mar 2014 21:48 UTCJuan Manuel Garriga

Thanks for your replies.

It's a very good help me.

3rd Mar 2014 22:30 UTCPhil M. Belley Expert

Similar shaped amphiboles are relatively common in marbles, easy to confuse. Tabular morphology in forsterite is quite common (even dominant) in marbles.

3rd Mar 2014 22:48 UTCRob Woodside 🌟 Manager

Thanks Phil

6th Mar 2014 13:40 UTCDavid Rausch

Hi everyone!

I'm the buyer of this piece! I'm unsure with Forsterite, because I can't find any reference for luminescence. And as Juan said, it shows high activity under uv-light (lw)! Can anybody help me with this?

Thank's!

David

6th Mar 2014 15:05 UTCTimothy Greenland

Hello David,

Here is a link to the luminescence of forsterite:

http://www.fluomin.org/uk/fiche.php?id=353

Hope this helps.

Tim

6th Mar 2014 19:55 UTCDavid Rausch

Thanks allot Tim!

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