Identity HelpGem silica, chalcedony, chrysocolla ... or what?
On behalf of a fellow Gem Club member, I am trying to identify this stone. The photo attached shows the stone both in rough and polished states. It appears to be a dendritic or mossy chrysocolla encrusted upon - and embedded within - a silky gray chalcedony. My friend is calling it gem silica but I don't think it meets the criteria, even though it is a very lovely stone.
Base mineral - we think chalcedony
Luster - silky
Color - gray
Streak - white
Hardness - 6
Crystalline structure - fine, microscopic, I don't know
Locale - Hinsdale County, Colorado, a vertical vein, may have been a pyroclastic layer
Specific gravity - I don't know
Acid test - no reaction using 5% vinegar
Surface mineral - we think chrysocolla but I do not know what white areas are
Luster - opaque
Color - blue, green, white
Streak - white
Hardness - 4
Crystalline structure - dendritic or mossy, does not flake or crumble off
Locale - same as above
Specific gravity - I don't know
Acid test - no reaction using 5% vinegar
At this point, we believe it is new semiprecious stone for Colorado - but I don't understand the criteria for such things. It looks similar to photos of heliotrope but I don't see the chrysocolla bloom on photos of heliotrope which this stone has.
Thanks for your help
Jama
Four Corners Gem and Mineral Club
Durango CO
Hi Jama,
Did you try to see if the stone is fluorescent at all? The sample to my eyes would seem to resemble some sort of moss agate... There are moss agate occurrances in quite a few US states, it appears.
The grey-blue-greenish material might be a bit tricky to identify without any analysis, but let's see what ideas the others come up with.
Cheers,
Joel Thank you. I will try to check fluorescence tomorrow at Gem Club.
Most of his polished stones resemble the center picture, almost always with that silky semi-transparent gray underneath and a thin colorful layer on top. (The amount of white in the final specimen is not his normal find).
Here is a little more info about the formation. The vein is thin. When he slabs it, he usually slices right down the middle of the gray vein. The blue green inclusions formed against the outside wall of the vein in contact with the pyroclastic layer. The blue green inclusions almost never deeply penetrate the translucent gray mineral within, like the inclusions on a moss agate might. If you aren't careful, the thin outer blue green layer can be entirely polished off, leaving one with a plain gray stone. Perhaps celadonite, which sometimes is found as a coating on agates. It forms early on in the vesicles, from decomposition of iron minerals in the matrix. Celadonite is soft, but some could be incorporated in the outer layer of agate. Visually, this strikes me as celadonite in chalcedony as well, although the hardness of 6 rather than 7 has me scratching my head. I could be wrong about hardness - I stopped at 6 when the stone scratched glass. I will look up celadonite. Thanks so much. I did not get to check fluorescence yet - don't think I can make that trip to gem club today. Jama,
While it does look like chrysocolla in Quartz it is not gem silica which is chrysocolla infused quartz. Gem silica would look more like gummy blue chrysoprase or the popular blue chalcedony which has that diffused, translucent quality. Yours has a more solid inclusion which shows some structure.
Hope this helps,
Gary
