Stephanite Composition, Crystallization and Structure

Composition. Sulphantimonite of silver, Ag5SbS4 or 5Ag2S. – Sb2S3 = sulfur 16.3, antimony 15.2, silver 68.5.

Crystallization. Orthorhombic. Crystals usually short prismatic and tabular parallel to the base. Edges of Crystals truncated by various pyramids. Prism zone usually shows the four prism faces and the two of the brachypinacoid, all making nearly 60º angles with each other and so giving the crystals a hexagonal aspect. Also twined in pseudohexagonal crystals. Crystals usually small.

Structure. Massive, in disseminated grains; crystallized.

Physical Properties. H. = 2-2.5 G. = 6.2-6.3. Metallic luster. Color and streak iron- black.

Tests. Fusible at 1. B. B. on charcoal gives dense white sublimate of antimony trioxide and odor of sulphur dioxide. Decomposed by nitric acid, and if after filtering a little hydrochloric acid is added to filtrate, it gives a white precipitate of silver chloride. Recognized by its stout hexagonal crystals and the above tests.

Occurrence. A rare mineral of primary origin but characteristically found in the upper potions of its veins. Found associated with other sulphantimonites of silver, galena, tetrahedrite, sphalerite, etc. occurs at Freiberg and other localities in Saxony; in Czechoslovakia; at Guanajuato and Arizpe, Sonora, etc., Mexico; in Chile. In the United States was an abundant ore at the Comstock Lode and other silver deposits in Nevada.

Use. An ore silver.