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Rosette of Bladed Polybasite

The Mineral polybasite




Polybasite is an uncommon mineral containing silver and copper in its structure. It is almost always found in known silver deposits, often in association with Stephanite. Polybasite forms a series with Pearceite, with Polybasite being the antimony-rich member, and Pearceite being the arsenic-rich member. It is often not possible to visually distinguish these two minerals from each other. Polybasite is named from the Greek words, poly, "many" and basis, "base" referring to its composition of several metallic and submetallic elements.
Chemical Formula [(Ag9CuS4)][(Ag,Cu)6Sb2S7]
Composition Silver and copper antimony sulfide, often with some arsenic
Variable Formula [(Ag9CuS4)][(Ag,Cu)6(Sb,As)2S7]
Color Dark gray to nearly black. May have occasional internal red reflections or iridescence.
Streak Black. May have a red tinge.
Hardness 2 - 3
Crystal System Monoclinic
3D Crystal Atlas
(Click for animated model) 
Crystal Forms
and Aggregates
Most often pseudohexagonal in shape, due to twinning on the prism-planes. Crystals are usually tabular, platy, bladed, or in rosette habit. Often striated with triangular striation patterns. Also grainy, flaky, and massive.
Transparency Opaque
Specific Gravity 6.0 - 6.2
Luster Metallic
Cleavage 1,1
Fracture Uneven
Tenacity Brittle
In Group Sulfides; Sulfosalts
Striking Features Crystal habits, streak, and mode of occurrence.
Environment Low temperature epithermal veins in silver ore deposits.
Rock Type Sedimentary, Metamorphic
Popularity (1-4) 3
Prevalence (1-3) 3
Demand (1-3) 1


Polybasite AUCTIONS

VARIETIES
 -  A polytype of Polybasite, with the same chemical formula but different crystal structure. Polybasite-Tac is therefore classified as an individual mineral species. Polybasite-Tac was previously known as Antimonpearceite, and was renamed by the IMA in 2006.


USES
An ore of silver and rare collector's mineral.

NOTEWORTHY LOCALITIES
Polybasite is not a common mineral. In Europe, well-formed micro hexagonal crystals come from the Clara Mine, Rankach valley, Oberwolfach, Baden-Württemberg, Germany. Small flaky crystals have come from the Příbram area, Bohemia, Czech Republic. In Peru, Polybasite occurs with Pyrargyrite at the Uchucchacua Mine, Oyon Province, Lima Department.

Mexico contains several notable localities for this mineral. Large, well-formed crystals of Polybasite have come from the San Juan de Rayas Mine, Guanajuato; and large single crystals and groups from the Chispas Mine, Arizpe, Sonora. Crystal clusters with Calcite have come from the Proano Mine, Fresnillo, Zacatecas.

Polybasite is very rare in U.S.: Crudely formed crystal clusters have come from the Eagle Mine, Gilman, Eagle Co., Colorado. In Canada, exceptional, well-formed, iridescent crystals came from a small find Husky Mine, Elsa, Galena Hill, Mayo Mining District, Yukon Territory. Small crystals and flakes come from Cobalt, Timiskaming District, Ontario.

COMMON MINERAL ASSOCIATIONS
Quartz, Galena, Chalcopyrite, Calcite, Stephanite, Silver, Pyrargyrite

DISTINGUISHING SIMILAR MINERALS
Hematite - Has a greater hardness, redder streak, and is slightly attracted to magnets.
Stephanite - Difficult to distinguish, although crystals are usually thicker.
Pearcite - Indistinguishable without complex methods.


polybasite PHOTOS
 
ADDITIONAL RESOURCES
 
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