Ajoite-Chrysocolla Mixup

Write By: tmmadmin Published In: Mineral Species Created Date: 2016-04-13 Hits: 1994 Comment: 0


3.6" Neon Aqua-Blue CHRYSOCOLLA CRYSTALS Pseudo Malachite/Azurite D.R.Congo for sale

I knew I should have trusted my initial instincts. It was early February out in Tucson, and I saw a specimen labeled "Ajoite Pseudo after Azurite" in a dealer's display case. The problem was that I had been selling the exact same material for several years, and had always labeled it as "Chrysocolla Pseudo after Azurite." Max Mpuye had been selling me great specimens of this colorful material since it first appeared at the East Coast Show in 2012. Here's how I described one of the specimens:

Most references say that chrysocolla does not form crystals. But this piece, part of a small find in the Congo, appears to prove otherwise. The piece is covered with shaggy little crystals, all colored a deeply saturated, very eye-catching bright turquoise. They are arrayed as an outer epimorph coating over pseudomorphs of chrysocolla after azurite, and over a thick, 1" long mess of noodle shapes (probably pseudomorphs of something like aragonite).

2.2" Screamin' Turquoise CHRYSOCOLLA Crystals Pseudo Malachite/Azurite Congo for sale

You can imagine my surprise when I saw the "ajoite" label, and more than surprise - incredulity. The dealer assured me that it had just been tested at the mineral lab at the University of Arizona (U of A), and it was in fact ajoite, not chrysocolla. Really? So suddenly these specimens were worth two to three times as much because they are ajoite?

Ajoite is (K,Na)Cu7AlSi9O24(OH)6·3H2O, hydrated sodium potassium copper aluminium silicate hydroxide, a rare copper silicate named after the type locality, the New Cornelia mine in Ajo, Arizona, USA. Chrysocolla, on the other hand, is Cu2-xAlx(H2-xSi2O5)(OH)4·nH2O, a hydrated copper phyllosilicate mineral. To add to the confusion, chrysocolla is difficult to analyze properly. Mindat says:

The name [chrysocolla] is often used for any massive, globular, glassy, commonly blue to green and sometimes black or rarely yellow copper-bearing silicate minerals which have not been specifically identified as to species. Multiple analyses of different compositions have been offered over the years. Chrysocolla is usually X-ray amorphous with crystallites too small to give a crystal's diffraction pattern.

2.4" Electric Turquoise CHRYSOCOLLA Crystals Pseudo Malachite/Azurite Congo for sale

Then on March 18 of 2016, Isaias Casanova reported on the Mindat messageboard that, "I just had the U of A do a series of formal tests [raman and chemical] on the chrysocolla/ajoites from the Congo and the results came back. It is not ajoite, there is no potassium or sodium, essential elements in ajoite. It is chrysocolla." The same day, Bruce Cairncross replied, asking if the analysis was of the tiny stalagmite-looking crystals that stick out all over the pseudomorphs of malachite after azurite. Cairncross cited a U of A study by Dr. Hexiong Yang of the U of A mineral lab, who did the testing and who said it was ajoite. The next day, Brian Kosnar reported that Yang on March 10 had clarified, "Bob Downs just pointed out to me that we do not have the confirmed ajoite in our RRUFF database yet. Therefore, I should have said that the Raman spectrum of your sample matches that of our unconfirmed "ajoite" samples." At the end of March, Mike Eggleston repeated the testing at Colgate University's lab, and the results confirmed that the material is in fact chrysocolla.

3" CHRYSOCOLLA Crystals Pseudo Malachite/Azurite From the New Find Congo for sale

Now that the brouhaha has died down, we are back where we started. The material is chrysocolla, formed as encrustation pseudomorphs of malachite after azurite. The color is still an exceptionally bright electric turquoise blue. And the formations are very three-dimensional and dramatically sculptural, with pseudomorph fingers sticking up from the crusty matrix. Neat stuff!

So like I said, I should have trusted my instincts. Especially since I have had to revisit and revise all my listings for "ajoite" and make them chrysocolla instead. One bright spot in this ignoble saga: no one bought any of the "ajoite" specimens from me, so at least I don't have to go back and apologize and make amends.

If you want, you can follow the entire Mindat messageboard conversation here: http://www.mindat.org/mesg-11-377662.html

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