Azurite

azurite

smithsonite

malachite

cuprite

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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 Lin Ma Hang mine, North District, New Territories, Hong Kong, China, the lead-zinc deposit is a hydrothermal deposit which lies along a fault zone within altered acid volcanic rocks, consisting mainly of chlorite, biotite, sericite and actinolite, with scattered quartz. (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)
The mineralisation consists of a series of fissure vein deposits varying from a few mm to several metres on width. The initial vein filling was coarse milky quartz. this was followed by an intrusion of fine-grained quartz carrying the metallic minerals, galena, pyrite, sphalerite and chalcopyrite, in order of abundance (Geological Society of Hong Kong Newsletter, 9.4.3-27).
Malachite and azurite are occasionally found in close association with chalcopyrite

The Ma On Shan Mine, Ma On Shan, Sha Tin District, New Territories, Hong Kong, China, is an abandoned iron mine, with both underground and open cast workings. The iron ores contain magnetite as the ore mineral and occur predominantly as masses of all sizes enclosed in a large skarn body formed by contact metasomatism of dolomitic limestone at the margins of a granite intrusion. In parts of the underground workings magnetite is also found in marble in contact with the granite. The skarn rocks consist mainly of tremolite, actinolite, diopside and garnet. Malachite and azurite are occasionally found in close association with chalcopyrite, formed by the action of carbonated water on the chalcopyrite
(Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

The Lin Fa Shan deposit, Tsuen Wan District, New Territories, Hong Kong, China, is located in a remote area of the Tai Mo Shan Country Park, on a steep west facing slope of Lin Fa Shan, just above the abandoned village of Sheung Tong. The surrounding hillsides are covered with shallow excavations, representing past searches for wolframite, the natural ore of tungsten. The abandoned workings are extremely dangerous with unsupported tunnels, open shafts and no maintenance since their closures in 1957; the workings should not be entered (http://industrialhistoryhk.org/lin-shan).
Malachite and azurite are occasionally found in close association with chalcopyrite formed by the action of carbonated waters on the chalcopyrite (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council).

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).

From the Ting Tang Mine, Carharrack, Cornwall, England, UK, specimen BM.1964,R6776 from the Natural History Museum, London, is an unusual specimen showing a banded cross-section of a cavity lined initially by what might be malachite and sequentially infilled with : two generations of distinctly coloured brown to tan columnar radiating crystals assumed to be olivenite, undetermined poorly crystalline green phases and a central core of coarsely crystallised dark blue azurite (RES2 p129).

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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