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Stephanite Mineral Facts:
Chemical
Formula: Ag5SbS4
Stephanite is 68.5% Silver by
weight.
Colors:
Dark Gray to black.
Its streak is black.
Hardness: 2
.
Density: 6.2 to 6.3
Cleavage:
The cleavage
is perfect parallel to (010) and the fracture uneven.
Crystallography: Orthorhombic
Stephanite crystallizes in hemimorphic orthorhombic crystals. The
crystals are highly modified, 125 forms having been identified upon
them. They have usually the habit of hexagonal prisms, their predominant
planes.
Crystals are usually small. Also twinned in pseudohexagonal
crystals.
Luster:.
Sub-metallic to metallic
Optics:
(Refractive Index) Opaque
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Composition,
Structure and Associated Minerals:
Stephanite, though a
comparatively rare mineral, is an important ore of silver in some mining
camps. It is found associated with other sulphantimonites of silver, etc.
Crystals
usually short prismatic and tabular parallel to the base.
It occurs massive, in
disseminated grains and as aggregates of small crystals. Analyses indicate a
composition very close to the requirements of the formula Ag5SbS4.
Identification and Diagnostics
On charcoal stephanite fuses very
easily to a dark gray globule, at the same time yielding the white fumes
of antimony oxide and the pungent odor of SO2 . Under the reducing flame
the globule is reduced to metallic silver. The mineral dissolves in
dilute nitric acid and this solution gives a white precipitate with HCl.
Stephanite is easily distinguished from other black minerals by its easy
fusibility, its stout hexagonal crystallization, and its reactions for
Ag, Sb and S.
Occurrence,
Localities and Origins:
The mineral is
associated with other silver ores in the primary ores and the secondary zone
of enrichment of veins at Freiberg, Saxony; Joachimsthal and Pribram,
Bohemia; at Guanajuato and Arizona, Sonora, etc., at many points in
Mexico, Peru and Chile and other mines in the Rocky Mountain region and at
many points in Mexico and Peru. It is particularly abundant in the ores of
the Comstock Lode, and other silver deposits in Nevada, and of the Las
Chispas Mine, Sonora, Mex. It is formed at low to moderate temperatures.
It is mined
together with other silver bearing minerals as an ore of silver.
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Stephanite and Pyrargyrite Silver Ore, Nevada |
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