Azurite

azurite

smithsonite

malachite

cuprite

Images

Formula: Cu3(CO3)2(OH)2
Anhydrous carbonate containing hydroxyl, copper-bearing mineral
Specific gravity: 3.77
Hardness: 3½ to 4
Streak: Light blue
Colour: Deep blue
Solubility: Azurite is moderately soluble in hydrochloric, sulphuric and nitric acid
Environments:

Carbonatites
Hydrothermal environments

Azurite is less common than malachite but has the same origin and associations. It is a secondary mineral found largely in the oxidation portions of high temperature copper deposits.

It may be found in gneiss.

Localities

The Two Mile and Three Mile deposits, Paddy's River, Paddys River District, Australian Capital Territory, Australia, are skarn deposits at the contact between granodiorite and volcanic rocks. azurite is a secondary carbonate that occurs with malachite on oxidised magnetite, and as crystals to 2.5 mm in anthophyllite-magnetite rocks (AJM 22.1.42).

At the Mount Kelly deposit, Gunpowder District, Queensland, Australia, the copper ores overlie primary zone mineralisation consisting of quartz-dolomite-sulphide veins hosted in siltstone and schist. Azurite is associated with chrysocolla and malachite (AJM 22.1.22).

At the Chessy copper mines, Chessy-les-Mines, Villefranche, Rhône, Auvergne-Rhône-Alpes, France, azurite pseudomorphs after cuprite (KL p176), and malachite pseudomorphs after azurite have been found (R&M 95.3.275).

At Tsumb, Namibia, azurite is mostly partially or wholly altered to malachite; unaltered azurite crystals are much less common (R&M 93.6.540). Smithsonite and tennantite pseudomorphs after azurite have been found here (KL p1676, R&M 95.3.275).

At the Snelston mine, near Ashbourne, Derbyshire, England, UK, azurite is associated with malachite and cerussite in a sandstone matrix (RES p140,141).

At the Bardon Hill quarry, Coalville, Leicestershire, England, UK, azurite is associated with malachite in dacite (RES p193).

At the New Cliffe Hill quarry, Stanton under Bardon, Leicestershire, England, UK, azurite has been found associated with malachite and vésigniéite, and also with malachite, cuprite and native copper (RES p195, 196).

At Cloud Hill quarry, Breedon on the Hill, Leicestershire, England, UK, azurite has been found associated with chalcopyrite, goethite and dolomite (RES p208).

At the Westcott mine, Pulverbatch, Shropshire, England, UK, azurite has been found associated with chalcocite (RES p289).

At the Llynclys quarry, near Oswestry, Shropshire, England, UK, azurite has been found in cavities in chalcopyrite - goethite veinstone, with minor malachite (RES p294).

At Judkins quarry, Nuneaton, Warwickshire, England, UK, azurite has been found coating calcite (RES p294).

At the Campbell mine, Bisbee, Arizona, USA, malachite pseudomorphs after azurite have been found (KL p179).

Amity, Town of Warwick, Orange county, New York, USA, is an area of granite intrusions into marble and associated gneiss. The marble is mostly composed of white crystalline calcite that often has small flakes or spheres of graphite and phlogopite. Azurite was found in a single boulder in marble as a bright blue wavy band associated with malachite (R&M 96.5.435).

At the Apex mine, Jarvis Peak, Beaver Dam mountains, Washington county, Utah, USA, an azurite and malachite pseudomorph after gypsum has been found (KL p177).

Alteration

Azurite is formed by the action of carbonated water on copper-containing minerals, or from copper-containing solutions, such as CuSO4 or CuCl2 reacting with limestone.

azurite and H2O to malachite and CO2
2Cu3(CO3)2(OH)2 + H2O → 3Cu2(CO3(OH)2 + CO2
Azurite is unstable under atmospheric conditions, and slowly converts to the more stable malachite according to the above reaction.

The Activity-pH diagram below was calculated at 298.2 K for some carbonates and copper arsenates for constant activity (roughly equivalent to concentration) of H2AsO4- in solution, over a range of values of pH and of H2CO3 activity (MM 52.687).
stability AsO4, CO3.jpg

The mineral formulae are:
azurite: Cu3(CO3)2(OH)2
malachite: Cu2(CO3)(OH)2
olivenite: Cu2(AsO4)(OH)
cornubite: Cu5(AsO4)2(OH)4
clinoclase: Cu3(AsO4)(OH)3













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