THE MINERAL STEPHANITE

Chemistry: Ag5SbS4, Silver Antimony Sulfide
Class: Sulfides
Subclass: Sulfosalts
Uses: An ore of silver and as mineral specimens.
Specimens

Stephanite is an uncommon silver bearing mineral that is named after a onetime Archduke of Austria, Victor Stephan. Although not a well known ore of silver, it is never-the-less a locally important ore in some mines. Stephanite typically forms nicely shaped crystals that are tabular to short prismatic. Its crystals can have a pseudohexagonal outline making them look like crystals of polybasite, a closely related mineral. Stephanite lacks polybasite's rhombic striations on its pinacoidal faces, good cleavage and the red flashes.

PHYSICAL CHARACTERISTICS:

Color is an iron black to dark gray.
Luster is metallic.
Transparency: Crystals are opaque.
Crystal System: Orthorhombic; 2 m m
Crystal Habits include tabular or short prismatic crystals that are dominated by prominent pinacoidal faces. Crystals are sometimes intergrown and form pseudohexagonal plates. Also as disseminated grains and massive.
Cleavage is poor in two directions.
Fracture is conchoidal to uneven.
Hardness is 2 - 2.5
Specific Gravity is approximately 6.2 - 6.3 (heavy even for metallic minerals)
Streak is a black.
Other Characteristics: Dark coating can often form after prolonged exposure to light (can be removed by ultrasonic treatment) and crystals tend to be striated perpendicular to the prominent pinacoids.
Associated Minerals include silver, proustite, pyrargyrite, polybasite, sphalerite, quartz, barite, calcite, pyrite, fluorite, galena, tetrahedrite , acanthite and other silver sulfide minerals.
Notable Occurrences include Sonora, Mexico; Freiberg, Saxony, Germany; Colorado, California and Comstock, Nevada, USA; Atacama, Chile; Cobalt, Ontario, Canada; Cornwall, England and Bolivia.
Best Field Indicators are good crystal habit, density, softness, association with other silver sulfosalts and lack of cleavage.