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GeneralQuestion about Allophane and Chrysocolla
18th Apr 2024 22:27 UTCRolf Luetcke Expert
Mindat on both minerals lists that the mineral may be the other species. So, looked at photos, books and more but have not found just how to easily tell one from the other?
Anyone have any ideas?
18th Apr 2024 23:06 UTCAlfredo Petrov Manager
19th Apr 2024 15:04 UTCGünter Frenz Expert
19th Apr 2024 15:41 UTCMichael Hatskel
It is my understanding from the literature that the behavior in HCl is different: Allophane decomposes relatively faster and forming SiO2 gel; Chrysocolla decomposes with more difficulty and forming non-gelatinous residue.
Disclaimer: haven't tested it myself.
And not sure how a mixture of the two minerals will behave.
19th Apr 2024 19:27 UTCAlfredo Petrov Manager
Michael Hatskel ✉️
Chrysocolla decomposes with more difficulty and forming non-gelatinous residue. I suspect that such chrysocolla is mixed with chalcedony, which is often the case - ie. the "chrysocolla" used for lapidary work rather than mineralogical chrysocolla.
19th Apr 2024 16:31 UTCRolf Luetcke Expert
I did notice on the main Allophane photos on mindat, none listed Chrysocolla with the Allophane.
Still quite interesting to me.
Thank you for your input so far.
19th Apr 2024 20:58 UTCRolf Luetcke Expert
19th Apr 2024 20:59 UTCRolf Luetcke Expert
19th Apr 2024 21:56 UTCRalph S Bottrill 🌟 Manager
20th Apr 2024 02:53 UTCPatrick Haynes (2) Expert
Your bright blue opaque (?) material looks like chrysocolla.
20th Apr 2024 14:03 UTCRolf Luetcke Expert
I looked over the pieces I broke under the microscope and even the opaque material was not chrysocolla. That is why this whole subject came up for me, I studied the material closely and determined it was actually "all" allophane.
Thank you for your Graphic Mine material work, I collected there many years ago.
20th Apr 2024 16:57 UTCPatrick Haynes (2) Expert
I have two pretty sweet Arizona chrysocolla specimens. They both very slowly shed flakes of material, probably from surficial dehydrating. In about two hunded years they may not be the same sweet specimens.
It is not uncommon to see shrinkage cracks in thin layers of chrysocolla. Allophane does seem to crack up more easily from dehydration than chrysocolla.
There was a third clay-like component in the Graphic specimens that I had tested, but it was minor, increasing in the chalky white gibbsite-rich material. The allophane that I had tested was from an isolated place inside the mine. My results are only good for what I collected.
It is not generally safe to visually ID allophane. There are other minerals that it could be besides chrysocolla, it could be chalcoalumite or something else.
I am mentioning the following for everybody out there- The NMBGMR offers xrd services. The prices are variable. You can email Kelsey McNamara for estimates. Often somebody will send in a fist-sized rock and ask something along the lines of "What are the black specks in the middle of the rock?". People don't understand that xrd samples require preparation, resulting in a pinch of only the questionable item. Instead of paying somebody else to break down the rock, and isolating the questionable grain(s) with a microscope, which could take a couple of hours, save yourself some money by doing it yourself. Using a small container, like a micromount box or a capsule, send in only grains of the material that you question. If the material is ready to be crushed it will save the preparer a lot of time, also increasing the likelihood of it getting into "the pipeline" and tested quicker.
20th Apr 2024 22:02 UTCRalph S Bottrill 🌟 Manager
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