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PHARMACOSIDERITE

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Originally appearing in Volume V21, Page 355 of the 1911 Encyclopedia Britannica.
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PHARMACOSIDERITE , a See also:

mineral See also:species consisting of hydrated basic ferric arsenate, 2FeAsO4 Fe(OH)3.5H2O. Crystals have the See also:form of small, sharply defined cubes of an See also:olive- or grass-See also:green See also:colour, and occur together in considerable See also:numbers on the See also:matrix of the specimens. On See also:account of its cubic form the mineral was See also:early known as " See also:cube ore " (Ger., Wilrfelerz); the name pharmacosiderite, given by J. F. L. See also:Hausmann in 1813, alludes to the See also:arsenic and See also:iron See also:present (4 fipaaKov, See also:poison, and rL pos, iron). The faces of the cube are striated parallel to one See also:diagonal, and alternate corners are sometimes replaced by faces of a See also:tetrahedron. The crystals are feebly doubly refracting, and in polarized See also:light exhibit a banded structure parallel to the cube faces. The hardness is 22 and the specific gravity 2.8. See also:Recent analyses prove the presence of a small but variable amount of See also:potassium (See also:K20, 2.68—4.13%) in the Cornish crystals, though in those from See also:Hungary there isonly a trace; this constituent appears to take the See also:place of basic See also:hydrogen in the above See also:formula. A curious See also:property is to be observed when a crystal of pharmacosiderite is placed in a See also:solution of See also:ammonia—in a few minutes the green colour changes throughout the whole crystal to red; on placing the red crystal in dilute hydrochloric See also:acid the green colour is restored. Natural crystals are sometimes See also:honey-yellow to See also:brown in colour, but this appears to be due to alteration.

Pharmacosiderite is a mineral of secondary origin, the crystals occurring attached to gozzany See also:

quartz in the upper See also:part of See also:veins of See also:copper ore. It was found in some abundance at the end of the 18th See also:century in the copper mines of the St See also:Day See also:district in See also:Cornwall, and has since been found at a few other localities, for example, at See also:Konigsberg near Schemnitz in Hungary, and in the Tintic district in See also:Utah. (L. J.

End of Article: PHARMACOSIDERITE

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