It's a Mystery to me

Good Morning everyone,

I have a mystery on my hands and while I know a picture, in this case, is NOT worth a thousand words, it is pretty much all I have to go on.

This little beauty was handed to me in a plastic bag. The bag says 12, 2 g $170.00

Now, I weighed it right away and it is obvious that the bag it is in, is NOT the correct bag, as this piece only weighed 0.5 grams.

It is triangular in shape with faces on the side. It appears to be black with some silverish material, but when you put a light behind it, it is obviously a deep blood red.

The sides are 11mm x 10mm x 11mm

I do not know its location or in fact anything else about it.

Based on the books I do have available, it looks sort of like Pyrargyrite to me? I am sorry I cannot provide hardness or other details. I simply do not know.

Any help or direction would be greatly appreciated.

sincerely,
Mira



Edited 1 time(s). Last edit at 06/13/2012 02:10PM by Mira Bai.

Hi Mira,

In the absense of any hardness, streak or SG readings, my guess is alexandrite.

compare to this one in the gallery:

[www.mindat.org]

regards,
stephanie



Edited 1 time(s). Last edit at 06/13/2012 02:53PM by Stephanie Martin.

Hey Steph,

Thanks for the suggestion. I thought about Alexandrite but it does not have that color change like alexandrite does. What I think is confusing me more is the triangular shape of the crystal. Since it is not my crystal, I am not comfortable scratching it for hardness. I need to educate myself on what "streak" means (not the nekkid kind I would imagine).

I know it is a challenge. A friend I know just handed it to me and said, what is it and how much is it worth? ROFL Doh!

Hello Mira,

It sure is a beauty. It Clearly is a chrysoberyl twin and the green/red color makes it a nice Alexandrite crystal. These crystals grow in a dense biotite rock hence the little flakes that appear to be still attached to the specimen. By the looks of it i think this crystal originates Brazil or Russia but thats hard to tell for sure. These nice V-twins with good color are not common.

Kind regards,
Peter

Hi Mira,
I agree with Peter and Stephanie, looks like a V twin alexandrite to me also.

Streak is when you drag the crystal across a surface (like the unglazed back of a tile) and look at the residue left by the crystal. (not the nekkid streaking ).

Hope this helps, and it really is a nice piece. What are the dimensions?

Warm regards,
Corie

Thanks everyone!! this is tremendously helpful! Measuring more accurately with my caliper, it is 2.75mm thick. The three sides measure, 11.2 mm, 11.6mm, and 9.85mm.

Can someone please explain V Twin? I have only seen twins as two crystals that are attached to each other and this looks like a single crystal, so a perfect opportunity for me to learn something new!!

I happen to have an unglazed tile here. Perhaps I will go streaking after all :)

Thanks again Steph, Peter and Corie! You have all been such a great help.....I am very grateful :)

and as a side note, I ran the crystal down the unglazed tile. It left a light black/gray mark on the tile.
I also measured ct weight which is 2.5 carats



Edited 2 time(s). Last edit at 06/13/2012 10:34PM by Mira Bai.

Reading your post I immediately thought of Pyrargyrite, so great minds think alike and fools seldom differ. However looking at the photo it appears to be a spinel twin. It isn't a V twin, there's no V!!! The reentrant angles are at the points and not distinct on your piece. Peter is right about the mica schist, so it came from a metamorphic environment, but I haven't seen this material before so I don't know where.

Hi Mira,

The crystal form and striations on the crystal as well as the translucent red colour and the remnants of the matrix are what made me say alexandrite. If you have a decent kitchen scale it would be not too difficult to do a specific gravity test. I'm not sure your streak test was correct as you may have streaked the matrix.

Here is a picture of one that I have in matrix, that looks similar to yours, this is from Brazil. The crystal is approx 1cm x 1cm





Edited 1 time(s). Last edit at 06/14/2012 12:10AM by Stephanie Martin.

Mira ,

Re V twinning, it is a type of twinning that does result in a V shape. This is not uncommon with chrysoberyl and rutile is another good example.

Here are some examples from the gallery of rutiles exhibiting this feature:

[www.mindat.org]

and

[www.mindat.org]

I will post more pictures later with chrysoberyl and spinel twins when I am free. I think Rob is suggesting it is a macle twin rather than a V twin. A macle twin is different, for an analogy, think of a sandwich with 2 pieces of bread and no filling, the bread representing crystals. Sometimes the crystals are offset and make for nice form.

duplicate post, sorry



Edited 1 time(s). Last edit at 06/14/2012 12:37AM by Stephanie Martin.

Thanks Stephanie. I shouldn't shoot off my mouth when I haven't seen the material. When I saw your photo I thought you had misidentified your triangle, but just to be sure I had a look at the chrysoberyl gallery. All who suggested a V twin of Chrysoberyl are quite right. The V may not be there, as Stephanie's photo shows, and it would be where the support is in Mira's second photo. Sorry for my mistake and thanks for the learning experience.

LOL I really do want to thank you all for entertaining my conundrum :) I have taken three more pictures, closer up which may help a bit? or not....but I had to try :) I don't really see a V or a twin? it looks more like a rough area? but I am learning, so accept any and all information you can give and have already shared :) Hope these pics help a bit :) pics 4 and 5 are front and up close. pic 6 is the back and a tad blurry (sorry)



Edited 1 time(s). Last edit at 06/14/2012 12:53AM by Mira Bai.

Hi All,

I agree on Chrysoberyl. The reentrant could be very small and simply obscured by unremoved matrix. Just an observation but it looks similar to specimens and material I've had from Carnaiba Mine. [www.mindat.org]

Ron





Edited 1 time(s). Last edit at 06/14/2012 12:53AM by Ronald John Gyllenhammer.

Oh, I see now! :)

Thanks Ron, You can see the V on the left of the 4th pic and at the bottom of the 5th. Mira must have removed the mica.

LOL, no I didnt :) The pic Ron used was the back side of the crystal where the Biotite was (pic 6 is the same side as pic 2). I am scared to do anything to it or with it since it is not mine :) I think my picture taking skills need to improve :)



Edited 1 time(s). Last edit at 06/14/2012 01:24AM by Mira Bai.

In the 6th the two arms of the V are clear.

ah, ok! i see it now......i moved it around a bit so the shiny biotite stuff would not show as much......you guys are the best!

Hi Mira,

Just to finish up with my twinning examples...

a typical chrysoberyl twin, showing a small notch at the re-entrant angle (top), from Brazil.



a dark chrysoberyl cluster that shows at least one such twin near top left, notch is easily noticed, cluster is from Zimbabwe.



Regarding macle twins, as explained above they can be twins that show a doubling effect, but when they are offset 180 degrees,
they can be quite beautiful, as in these spinel "Star of David" macle twins below. More on spinel law twinning can be found on this old thread:
[www.mindat.org]