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REO ORPIMENT, OR REALGAR. 535 It is translucent, but the crystals are semi-transpa rent, It yields an orange-yellow coloured streak. It is very solt. It is brittle. It is easily frangible. Specific gravity, 3.223, Muickenbnck; 3.225, Berg- nan; 3.3384, Brisson. Chemical Characters. It melts immediately before the blowpipe, and burns with a blue flame, giving out arsenical and sulphureous vapours. It generally leaves a minute and earthy resi due. Physical Character. It is idio-electric by friction, acquiring the resinous or Negative electricity. / Constituent Parts. ' Bannat. Arsenic, - - 69 Sulphur, - 100 Klaproth, Beit. b. v. 238. Geognostic Situation. It occurs in veins in primitive rocks, especially in gneiss and clay slate; also disseminated, with iron-py- rites or primitive dolomite, and in the craters and in fhe vicinity of volcanoes. It is usually accompanied with native arsenic, light rp d silver ore, galena or lead-glance; sometinjcs also I. 1 4 with