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DIOPTASE

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Originally appearing in Volume V08, Page 289 of the 1911 Encyclopedia Britannica.
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DIOPTASE , a rare See also:

mineral See also:species consisting of See also:acid See also:copper orthosilicate, H2CuSiO4, crystallizing in the parallel-faced herniahedral class of the See also:rhombohedral See also:system. The degree of sym- metry is the same as in the mineral See also:phenacite, there being orly ar See also:axis of triad symmetry and a centre of symmetry. The crystals have the See also:form of a hexagonal See also:prism m terminated by a rhombohedron r, the alternate edges between these being sometimes re-placed by the faces of a rhombohedron s. The faces are striated parallel to the edges between r, s and in. There are perfect cleavages parallel to the faces of a rhombohedron which truncate the polar edges of r: from the cleavage cracks See also:internal reflections are often to be seen in the crystal, and it was on See also:account of this that the mineral was named dioptase, by R. J. See also:Hauy in 1797, from Sioirrciav, " to see into." The crystals vary from transparent to translucent with a vitreous lustre, and are See also:bright See also:emerald-See also:green in See also:colour; they thus have a certain resemblance to emerald, hence the See also:early name emerald-copper (See also:German, Kupfer-Smaragd). Hardness 5; sp. gr. 3.3. The mineral is decomposed by hydrochloric acid with separation of gelatinous See also:silica. At a red See also:heat it blackens and gives off See also:water. The See also:fine crystals from See also:Mount Altyn-See also:Tube on the western slopes of the See also:Altai Mountains in the See also:Kirghiz See also:Steppes, See also:Asiatic See also:Russia, See also:line cavities in a compact See also:limestone; they were first sent to See also:Europe in 1785 by Achir Mahmed, a Bucharian See also:merchant, after whom the mineral has been named archirite.

More recently, in 189o, See also:

good crystals of similar See also:habit, but rather darker in colour, have been found with See also:quartz and See also:malachite near Komba in the See also:French See also:Congo. As drusy crystalline crusts it has! been found at Copiapo in See also:Chile and in See also:Arizona. Dioptase has occasionally been used as a See also:gem-See also:stone, especially in Russia and See also:Persia; it has a fine colour, but a See also:low degree of hardness and the transparency is imperfect. (L. J.

End of Article: DIOPTASE

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