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wolframite Ore mineral for tungsten, with the formula (Fe,Mn)WO4; sp. gr. 7.0–7.5; hardness 5.0–5.5; monoclinic; grey-black to brownish-black; brownish black streak; metallic lustre; crystals normally tabular, prismatic, often bladed, also occurs granular and massive; cleavage perfect quartz; occurs in high-temperature hydrothermal veins, quartz veins, and pegmatites, associated with granitic rocks, with cassiterite, arsenopyrite, tourmaline, scheelite, galena, sphalerite, and quartz.

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arsenopyrite (known historically as mispickel) Mineral, FeAsS; sp. gr. 5.9–6.2; hardness 5.5–6.0; monoclinic; silver-grey to white, often with a tarnish; dark greyish or black streak; metallic lustre; crystals prismatic, often striated, can also be massive and granular; cleavage distinct {101}; occurs in high- to moderate-temperature mineral veins in association with gold, ores of tin, tungsten, galena, and quartz, and also disseminated in limestones, dolomites, gneisses, and pegmatites. It is the principal source of arsenic compounds used for pest control, for the manufacture of dyes and chemicals, and in leather treatment.

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arsenopyrite (är´sĬnōpī´rīt, ärsĕn´ō–) or mispickel (mĬs´pĬkəl), silver-white to steel-gray mineral with the metallic luster characteristic of a pyrite. It is a sulfarsenide of iron, FeAsS, crystallizing in the orthorhombic system and occurring also in massive form. It is widely distributed and is an important source of arsenic. Often it is found associated with other minerals and ores of lead and tin. Saxony, Sweden, Cornwall, and various parts of the United States have important deposits.

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