Proustite - Light Ruby Silver
Composition, Crystallization and Structure

Composition. Sulpharsenite of silver, Ag₃AsS₃ or 3Ag2S.As₂S₃ = Sulfur 19.4, arsenic 15.2, silver 64.4. May contain a small amount of antimony. Compare pyrargyrite.

Crystallization. Orthorhombic. Crystals usually short prismatic to tabular. Sometimes quite complex with many prism, pyramid and dome faces. Frequently twined, giving tabular crystals with recurring reentrant angles in the prism zone (Fig. 239), whence the common name of cogwheel ore.

Structure. Massive; granular to compact; in crystals.

Physical Properties. H. = 2.5-3. G. = 5.7-5.9. Metallic luster. Color and streak steel-gray to black.

Tests. Fusible at 1. B. B. on charcoal gives a combination coating of antimony and lead oxides. Roasted in O. T. gives odor of sulfur dioxide and volatile crystalline sublimate of arsenious oxide. In C. T. gives abundante sublimate of arsenic sulphide, reddish black when cold. With sodium carbonate on charcoal gives a globule or silver. Characterized chiefly by its ruby-red color and streak and its brilliant luster.

Occurrence. A rare mineral, with mode of occurrence and associations similar to those of pyrargyrite. Found in the silver mines of Saxony; Bohemia; at Chañarcillo, Chile, in fine crystals; common in the solver mines of Peru and Mexico. Found in Colorado in the silver mines of the San Juan Mountains and elsewhere; in various silver district in Nevada, Idaho, etc.

Use. An ore silver