Adamite

minerals

zincolivenite

smithsonite

azurite

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Formula: Zn2(AsO4)(OH)
Anhydrous arsenate containing hydroxyl, olivenite group, orthorhombic paramorph of paradamite, which is triclinic. Forms a series with olivenite.
Specific gravity: 4.3 to 4.5
Hardness: 3½
Streak: White
Colour: Colourless, white, yellow, green (copper adamite), and pink to violet (cobaltoan adamite).
Solubility: Readily soluble in hydrochloric acid and sulphuric acid
Common impurities: Cu,Fe,Co

Environments:

Hydrothermal environments

Adamite is a secondary arsenate that occurs in the oxidation zone of high-temperature lode zinc and arsenic bearing hydrothermal mineral deposits, associated with austinite, azurite, calcite, limonite, hemimorphite, malachite, mimetite, olivenite, quartz, scorodite and smithsonite (Mindat).

Localities

At the type locality, the Chañarcillo Mining District, Copiapó, Copiapó Province, Atacama, Chile, adamite is associated with silver, limonite and chlorargyrite (Mindat).

At Tsumeb, Namibia, adamite is associated with smithsonite, goethite and zincolivenite (R&M 95.3.210-232).

At the Caldbeck Fells Mining Region, Cumbria, England, UK, adamite is rare. At the Deer Hills baryte mine it is associayed with agardite - mixite and aurichalcite. At the Driggith mine cuprian adamite has been found encrusting quartz. At Old Potts Gill mine it occurs with serpierite or malachite, and at Sandbeds mine it occurs as crystals or coatings on quartz (C&S).

Adamite is abundant and widespread at the San Rafael Mine, Nevada, USA. It usually occurs alone there, but it has been found associated with wulfenite and smithsonite, or with segnitite and duftite (R&M.85.6.514-515).

Alteration

legrandite to adamite and H2O
Zn2AsO4(OH). H2O (s) ⇌ Zn2AsO4(OH) (s) + H20(l)
Legrandite is a very much rarer mineral than adamite and it is suggested that it is in fact metastable with respect to adamite at room temperature, although it may crystallise as the stable phase under appropriate conditions at temperatures between 0 and 25oC. It is of interest that legrandite has been found at several localities without adamite (MM 52.685).

The Activity-pH diagram below was calculated at 298.2 K for some zinc arsenates and Ca3(AsO4)2 for constant activity (roughly equivalent to concentration) of Ca2+ ions in solution, over a range of values of pH and of Zn2+ activity (MM 52.685).
stability Zn.jpg

The zinc mineral formulae are:
adamite: Zn2(AsO4)(OH)
köttigite: Zn3(AsO4)2.8H2O
austinite: CaZn(AsO4)(OH)















The Activity-pH diagram below was calculated at 298.2 K for smithsonite, hydrozincite and adamite for constant activity (roughly equivalent to concentration) of H2AsO4- in solution, over a range of values of pH and of H2CO3 activity (MM 52.688).
stability smithsonite.jpg

The mineral formulae are:
smithsonite: Zn(CO3)
hydrozincite: Zn5(CO3)2(OH)6
adamite: Zn2(AsO4)(OH)














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