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CHRYSOCOLLA

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Originally appearing in Volume V06, Page 320 of the 1911 Encyclopedia Britannica.
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CHRYSOCOLLA , a hydrous See also:

copper silicate occurring as a decomposition product of copper ores. It is never found as crystals, but always as encrusting and botryoidal masses with 'a microcrystalline structure. It is See also:green or bluish-green in See also:colour, and often has the See also:appearance of See also:opal or See also:enamel, being translucent and having a conchoidal fracture with vitreous lustre; some-times it is earthy in texture. Not being a definite crystallized substance; it varies widely in chemical See also:composition, the copper See also:oxide (CuO), for example, varying in different analyses from 17 to 67%; the See also:formula is usually given as CuSiO3+2H2O. The hardness (2–4) and specific gravity (2.0–2.8) are also variable. It has recently been suggested that the material may really be a mixture of more than one hydrous copper silicate, since See also:differences in the microcrystalline structure of the different concentric layers of which the masses are built up may be detected. Various impurities (See also:silica, &c.) are also commonly See also:present, and several varieties have been distinguished by See also:special names: thus dillenburgite, from Dillenburg in See also:Nassau, contains copper carbonate; demidoffite and cyanochalcite contain copper phosphate; and pilarite contains alumina (perhaps as See also:allophane). The See also:mineral occurs in the upper parts of See also:veins of copper ores,and has resulted from their alteration by the See also:action of See also:waters containing silica in See also:solution. Pseudomorphs of chrysocolla after various copper minerals (e.g. See also:cuprite) are not uncommon. It is found in most copper mines. The name chrysocolla (from xpveor, See also:gold, and xoXXa, See also:glue) was applied by See also:Theophrastus and other See also:ancient writers to materials used in soldering gold, one of which, from the See also:island of See also:Cyprus, may have been identical with the mineral now known by this name. See also:Borax, which is used for this purpose, has also been called chrysocolla.

A mineral known as pitchy copper-ore (Ger. Kupferpecherz), and of some importance as an ore of copper, is usually classed as a variety of chrysocolla containing much admixed See also:

limonite. It is dark See also:brown to See also:black in colour, with a dull to glassy or resinous lustre, and resembles See also:pitch in appearance. In thin sections it is translucent and optically isotropic, and See also:recent See also:examinations seem to prove that it is a homogeneous mineral and not a See also:mechanical mixture of chrysocolla and limonite. (L. J.

End of Article: CHRYSOCOLLA

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