Evansite

evansite

variscite

allophane

wavellite

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Formula: Al3(PO4)(OH)6.8H2O
Hydrated phosphate containing hydroxyl
Specific gravity: 1.8 to 2.2
Hardness: 3 to 4
Streak: White, lightly tinted
Colour: Colourless, milk-white, lightly tinted blue, green or yellow at times; brown, reddish-brown, or red due to wüstite inclusions; colourless to brown in transmitted light
Solubility: Easily soluble in acids
Common impurities: Cu,Pb
Environments:

Metamorphic environments

Evansite is a secondary phosphate mineral that forms as a derivative of guano, usually in the form of cave fillings in graphite-containing deposits, gneiss and coal strata. Associated minerals include variscite, allophane and limonite (Wiki).

In the phosphate deposits of South Australia, evansite is usually associated with apatite, wavellite or turquoise (AJM 17.1.16).

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