Sulfides, Semimetals
Sulfides and Realgar
The sulfides form an important group of minerals which includes the majority of the ore minerals. With them are classed the similar but rarer selenides, tellurides, arsenides and antimonides. The sulfides may be divided into two groups depending upon the character of the metal present: (1) Sulfides of the Semimetals, (2) Sulfides of the Metals.
Sulfides of the Semimetals
Realgar
Composition. Arsenic monosulphide, AsS = Sulfur 19.9, arsenic 70.1.
Crystallizations. Monoclinic. Short prismatic crystals, vertically striated.
Structure. In crystals, coarse to fine granular, often earthy and as an incrustation.
Physical Properties. Cleavage parallel to clinopinacoid. H. = 1.5-2 G.= 3.55 Resinous luster. Color and streak red to orange. Transparent to opaque.
Test. Fusible at 1. Easily volatile. Heated on charcoal yields a volatile white sublimate of arsenious oxide with characteristic garlic odor. Roasted in O.T. gives volatile crystalline sublimate of arsenious oxide and odor of sulfur dioxide. Characterized chiefly by deep red color and resinous luster.
Occurrence. A rare mineral, occurring usually with orpiment, As2S3. Also associated with other arsenic minerals, stibnite, and with lead, silver, and bolds. Ores. Also occurs as a volcanic sublimation product or as a deposit form hot spring. Found associated with silver and lead ores in Hungary, Bohemia, Saxony, etc. Found in good crystals at Nagyag, Transylvania; Binnenthal, Switzerland; Allchar, Macedonia. Occurs at Mercur, Utah and at Manhattan, Nevada. Found deposited form the geyser waters in Yellowstone Park.
Name. The name is derived form the Arabic, Rahj al ghar, powder of the mine.
Use. Was used in fireworks to give a brilliant white light when mixed with saltpeter and ignited. Artificial arsenic sulfide is at present used for this purpose.
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