Disk shaped stone

[topazguy]

Hey all,

I am new to the boards, but I am hoping someone can help me identify this find.

I have turned up a number of disk shaped crystals near an ancient lava flow that have a slight green/yellow hue to them. They were in heavy clay (not rock) next to a number of lava boulders.

The crystals range in size from 1-2 inches in diameter and are fairly brittle. They are distinctly disk shaped and have a sharp edge all the way around.

I have never seen anything remotely like them, so I was hoping someone here could shed some light.

Thanks!

topazguy

Attachments:

[arappaho]

Well, you got my curiosity up.
Better pics would help, but maybe someone will know what they
are from your description.

[arappaho]

I was thinking Cristobalite. Might be what it is.
Check out this link, (hope it works),

en.wikipedia.org/wiki/Cristobalite

Would love to see some self-found Topaz sometime.

[topazguy]

Oh man, I knew I had come to the right spot! Thanks for the replies so far guys, most appreciated!

I apologize for the bad photo. I took a few more shots tonight, so I hope these will help:

home.comcast.net/~topazguy/site/

One other thing to note are that this crystal has perfect cleavage and can be snapped off in small sheets. It kind of makes me think of Muscovite, but I have never seen it form like this.

Thanks again all!

PS - I will definitely throw some pics up of my topaz collection. I have quite a bit from the Thomas Range, including some naturally occurring pink specimens

[arappaho]

Well, topazguy, I don't know what else to say but thanks for the
better pics. Maybe someone else will have an idea.

All I can say is because of the environment you found the pieces
in, I can't think of what else it might be. The second paragraph of
the link I posted speaks to the metastability of Cristobalite and
some of the other polymorphs of quartz. Could be it's just
weathering and falling apart like the layers of an onion.

It does seem to be behaving more like a Feldspar, but I'm going to
have to stick with the Cristo for now.
Cool find and thanks for sharing. Let us know if you find out something
else about it.
Joe

[topazguy]

Thanks again Joe! I really appreciate your help on this one.

I think you are onto it with the metastability of the mineral and the fact that I'm most likely looking at a polymorph of some kind. I will probably leave it at that, but will keep my eyes open and update the thread if anything else turns up.

I will be back in this same area sometime this spring, so I will see if I can turn a few more of these up. I will also pay a little closer attention to any other clues in the area... as I'm afraid I was focused on something else when I initially found these and didn't really give them much thought at the time.