Monday, February 25, 2008

A mineral, or lemon pie filling? - Adamite


Adamite (Zn2(AsO4)(OH) (or hydroxide zinc arseniate) is another beautiful mineral that is found in several locations around the world (Mexico, Chile, Namibia, etc.) in ore deposits rich in zinc, lead, and arsenic that have suffered oxidation, due to weathering and lixiviation, out of the percolating water. All the sulfides decompose, and the resulting rich-in-chemical elements low-temperature solution deposits near and beneath the original ore. One of the formed new minerals is a shiny and crystallized piece of art with a green color that varies considerably. The most beautiful specimens I have had the chance to collect come from the Ojuela Mine in Mapimi, state of Durango. Adamite is found hereby associated with hemimorphite, legrandite, goethite, limonite, cobalt-adamite (purple), calcite, pyrite, cuprite, malachite, hematite, and others I am sure I don't remember. If someone asked me to make does an Adamite crystal looks like to me, I'd say it does look like filling of a lemon pie, the one it used to be cooked from scratch by my late Grandmother in Guadalajara (fattening, but out of this world!).

Chemical Formula: Zn2(AsO4)(OH)

Composition:
Zinc 45.61 % Zn 56.78 % ZnO
Arsenic 26.13 % As 40.08 % As2O5
Hydrogen 0.35 % H 3.14 % H2O
Oxygen 27.90 % O

Molecular Weight = 286.71 gm
Locality: Ojuela Mine, Mapimi Durango Mexico; Chile, Atacama, Chañarcillo
Name Origin: Named after the French mineralogist Gilbert Joseph Adam (1795-1881).

Crystal System: Orthorhombic - Dipyramidal
Cleavage: [101] Good, [010] Poor
Color: Yellow, Green, Violet, Pink, Yellowish green.
Density: 4.3 - 4.5, Average = 4.4
Diaphaniety: Subtransparent
Fracture: Brittle - Generally displayed by glasses and most non-metallic minerals.
Habit: Druse - Crystal growth in a cavity which results in numerous crystal tipped surfaces.
Habit: Encrustations - Forms crust-like aggregates on matrix.
Habit: Tabular - Form dimensions are thin in one direction.
Hardness: 3.5 - Copper Penny
Luminescence: Fluorescent and phosphorescent.
Luster: Vitreous - Resinous
Streak: white
Fluorescent: Yes, crystals fluoresce green under SW ultra violet light

I hope you have a productive week, visit if you have a chance my updated website: Oscar el Mexicano, meantime, see you in my next posting.

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