Minerals atacamite

Frost RL, Martens W, Kloprogge JT, Williams PA (2002) Raman sepctroscopy of the basic copper chloride minerals atacamite and paratacamite implications for the study of copper, brass and bronze objects of archaeological significance. J Raman Spectrosc 33 801-806. 

Synthetic copper chloride hydroxide analogue of the mineral atacamite q.v. Cu2Cl(OH)3). It is polymorphous with the other copper chloride hydroxides, botallackite, chnoatacamite and paratacamite (qq.v.). 

ATACAMITE. This mineral is a basic chloride of copper corresponding to formula Cu2Cl(OH)3. Crystallizes in thin, orthorhombic prisms, may occur massive. Hardness, 3-3.5 sp gr, 3.76-3.78 luster, adamantine to vitreous color, green, streak, green transparent to translucent. 

Copper is a reddish metallic element (symbol Cu atomic no. 29). Its symbol derives from the Latin word cuprum, because it was originally discovered in Cyprus. It is widely found as different salts in minerals such as atacamite (chloride) azurite and malachite (carbonates) bornite, chalco-cite, chalcopjrite, stannite, tennantite, and tetrahedrite (sulfides) chalcanthite (sulfate) dioptase (silicate) erinite and olivenite (arsenates) tenorite (oxide) torbernite (phosphate) and zorgite (selenide). Copper is an essential constituent of several enzymes. It is carried in the blood by a specific copper-binding protein, ceruloplasmin. 

Because malachite and aurichalcite are carbonates, they will fizz when a bit of nitric or hydrochloric acid is added, due to the formation of carbonic acid and the snbseqnent evolution of CO2. Atacamite can be identified by treating a soln-tion of the mineral in nitric acid with silver nitrate. The chloride ion will react with the silver ion to form insolnble silver chloride (Table 8, solubility rule 3). 

Copper s relative abundance in the Earth s crust is about 50 mg/kg (i.e., ppm wt.), which is less than nickel and zinc. It occurs as a native element (4%), but the major part of its occurrence is as oxides minerals (10%) such as cuprite [Cu O, cubic] carbonates (5%) malachite [CuC03.Cu(OH)j, monoclinic] and azurite [2CuC03.Cu(0H)j, monoclinic] sulfide minerals (80%) chalcocite [Cu S, monoclinic], chalcopyrite [CuFeS, tetragonal], and bornite [CUjFeS, cubic] and in other rare minerals (1%) such as atacamite [CUjC OH), orthorhombic]. But only the oxide and sulfide minerals are used industrially as copper ores. Chile is the world s largest producer of copper, followed by the United States. 

The relative rarity of the mineral has led some authors to conclude that the symthetic analogue (copper chloride hydroxide, atacamite type, q.v.) was used as pigment and in fact there are mnnerous mediaeval recipes for preparing a green copper pigment with common salt. Of these perhaps the best known is that of Theophilus for viride sabum (q.v.). 

Church (1865) Church, A.H. Notes on a Cornish mineral of the atacamite group Journal of the Chemical Society 18 (1865) 212-214... 

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