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MISPICKEL, a mineral consisting of iron sulpharsenide, FeAsS; it contains 40% of arsenic, and is of importance as an ore of this element. It is known also as arsenopyrite or arsenical pyrites (Ger. Arsenikkies) : mispickel is an old name of German origin, and in the form Mistpuckel was used by G. Agricola in 1546. The crystals are orthorhombic, with angles similar to those of marcasite; they are often prismatic in habit, and the prism M is usually terminated by the deeply striated faces of an obtuse dome r. Twinning is not uncommon, the twinplanes M (no) and g (101) being the same as in marcasite. The colour of the mineral is silver-white or steel-grey, with a metallic lustre, but it is often tarnished yellow; the streak is greyish-black. The hardness is si-6, and the specific gravity 5-9-6-2.

Mispickel occurs in metalliferous veins with ores of tin, copper, silver, etc. It is occasionally found as embedded crystals, for example, in serpentine at Reichenstein, Silesia. In Cornwall and Devon it is associated with cassiterite hi the tinlodes, but is also found in the copper-lodes: well crystallized specimens have been obtained from the neighbourhood of Tavistock, Redruth and St Agnes. Mispickel is the principal source of arsenious oxide or the " white arsenic " of commerce (see ARSENIC) . The chief supplies are from Cornwall and Devon, and Freiberg in Saxony, and from Canada and the United States.

Danaite is a cobaltiferous variety of mispickel, containing up to 9% of cobalt replacing iron; it was first noticed by J. F. Dana in 1824 at Franconia in New Hampshire. This variety forms a passage to the species glaucodote, (Co,Fe)AsS, which is found as well-developed orthorhombic crystals hi copper ore at Hakansboda in Ramberg parish, Vestmanland, Sweden. Other species belonging to this isomorphous group of orthorhombic minerals are marcasite (FeS 2 ), lollingite (FeAsz), safflorite (CoAsj) and rammelsbergite (NLAsz). (L. J. S.)

Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)

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