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Identity HelpHelp with identification of a crystal

11th Jul 2010 13:04 BSTsamcat

Hello,


I was hoping someone could help me narrow down a crystal I have. The person I bought it from had no idea what it was or where it is from. The crystal is a maximum of 100mm long, roughly circular with a max diameter of 38mm coming to a broken point and appears to be made up of a series of needle like crystals approx 0.5mm in diameter. These are small and are easily broken and are clear in colour however they are white when powdered. They are easily powdered. The crystal does not scratch with a fingernail or copper but does so with nickel, gold etc. It appears fibrous like optic fibre and is translucent as a whole crystal but when the component crystals are broken off they are transparent. It feels very smooth,very splintery, no taste, no inclusions, consistent colouring, not soluble in water and no reaction to acid. I have provided a photo of the entire crystal and one of the small fragments. Are there any other tests I can perform to assist?


Thank you.

11th Jul 2010 13:45 BSTMichel Gadoury

Hello Samcat,

My first guess would be Anhydrite.


http://www.mindat.org/min-234.html


Good luck !

11th Jul 2010 15:19 BSTSteve Hardinger Expert

I'm not trying to be meaen when I say this but the first picture is of such poor quality as to be useless for identification purposes.


The second is gypsum (selenite). These 'cityscape' or 'cathedral' pieces are of natural gypsum but man-made shape, and quite common at shows of all sizes.

11th Jul 2010 15:20 BSTDana Slaughter

Hi Samcat,


It looks to me that it may be ulexite from Boron, California.


Dana

11th Jul 2010 15:22 BSTSteve Hardinger Expert

Ulexite is another excellent idea. If you can scratch it with your fingernail, it's gypsum. If not, ulexite is a good possibility.

11th Jul 2010 17:32 BSTScott Sadlocha

The first picture is not really helpful, and the second picture is a bit small. But based on that, and most of the description, I agree that it would seem to be gypsum. However, the hardness is off. Gypsum should be soft and very easy to scratch. As Dana mentioned, ulexite would be another possibility. Is there any area on the piece that is somewhat polished? Ulexite has optic properties that make its identification easier. It has been called TV rock because images underneath it are projected to its surface. If there is a polished surface, you can try running it over print to see if it "projects".

11th Jul 2010 21:35 BSTRock Currier Expert

What is shown in the second picture is a piece of satin spar gypsum from Morocco that has been shaped a little bit by the locals. They will make anything you want from this easily shaped material and the kind you have is a shape that has proved popular and salable to people who don't know much abut minerals like interior decorators, new age people etc. We have imported and sold hundreds of them and they can be see at many gem and mineral shows and undoubtedly on the net as well.

12th Jul 2010 04:13 BSTDan R. Lynch

I can say, almost without question, that this sample is gypsum, variety selenite. My family owns a rock and mineral shop and we constantly sell these "selenite castles" to tourists.

13th Jul 2010 03:34 BSTsamct

I've attached a much better picture of the entire crystal. Sorry the first was so poor. It was very hard to get a decent image due to it reflecting and refracting light.


For everyone who has said it was gypsum, there is no way as I have a sample of gypsum and I can scratch that with a fingernail. This can't even be scratched with a copper coin. It's almost like it has been made up of many many long thin needles of glass. I bought it not because of the shape even though it has obviously been artificially shaped but because of it's texture and fine crystalline structure. It feels very silky and the "needles" are all aligned at a perfect 90 degrees from the base. The second photo in my first post was said to be polished however it is a fragment of one of the "needles" the max width of these is less than 0.5mm.


Any further help would be most appreciated.


Dave

13th Jul 2010 04:25 BSTsamcat

Sorry I haven't been able to get a good picture of one of the needles as I've lost my memory card attachment and can only use a crappy camera phone which doesn't do it justice. I tried running a small "needle" like fragment over print and I can see the print however it is not magnified. It is very much like glass. I've seen photo's of satin spar gypsum and it does indeed look like satin spar gypsum. But is it harder than so called ordinary gypsum? Although looking at selenite castles it looks remarkably similar. But again I cannot scratch it with a fingernail. I have come across this article which seems to confirm Dana Slaughter's identification of Ulexite. "Microstructure characterization of one directionally oriented ulexite" Y.H. Ikuhara, S. Kondoh, K. Kikuta, S-I. Hirano J. Min Res Vol 13;3 pg 778-783.


However saying that it does indicate that ulexite has a hardness of 2.5 and can be scratched by a fingernail. Because of it's directionality I am assuming it can be scratched more easily in certain directions. Is that a correct assumption? I'm basing that on early university level chemistry and physics not something I majored in :-) and I certainly didn't major in materials engineering or chemistry.


For a 100% definitive confirmation I can take it to the University where I have had some rocks identified however I really just want a general idea. Essentially I have what I was seeking. It's either Ulexite or a form of Gypsum.


From the photo's I have supplied satin spar and selenite gypsum certainly appear to be very accurate however the harness doesn't match unless the directionality has made an impact.


Once again all of your expert help is appreciated.

13th Jul 2010 04:32 BSTCraig Mercer

Definitely Satin Spar

13th Jul 2010 11:26 BSTTimothy Jackson

Yep its satin spar, here is mine.

 
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