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Proustite  
Current inventory:  0 gems
 

  
Proustite is named to honor Joseph Louis Proust (1754–1826), celebrated French chemist.

Discovered in 1832;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Ag₃AsS₃

Silver Arsenic Sulfide

Molecular Weight:

494.72 gm

Composition:

Silver

65.41 %

Ag

Arsenic

15.14 %

As

Sulfur

19.44 %

S

100.00 %

Classification

Mineral Classification:

Sulfides

Strunz 8th Ed. ID:

2/E.07-10

Nickel-Strunz 10th Ed. ID:

2.GA.05

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
G : Sulfarsenites, sulfantimonites, sulfbismuthites
A : Neso-sulfarsenites, etc. without additional S

Related to:

Proustite Group. Proustite-Pyrargyrite Series. Trigonal domorph of Xanthoconite.

Synonyms:

Arsenical Red Silver, Arsenical Silver Blende, Light red silver ore  

Crystal Data

Crystallography:

Trigonal - Hexagonal Scalenohedral

Crystal Habit:

Crystals prismatic, to 8 cm; commonly rhombohedral with dominant {0112} or {1011}; also scalenohedral with prominent {1231}; massive, compact.

Twinning:

On {1014} to produce trillings; also common on {1011} and on {0001}, {0112}.

Physical Properties

Cleavage:

Distinct on {1011}

Fracture:

Conchoidal to Uneven

Tenacity:

Brittle

Moh's Hardness:

2.0 - 2.5; VHN = 70–105 (25 g load)

Density:

5.57 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Exposure to light causes Proustite to turn black. This is a photochromic effect due to the presence of silver. So Proustite should not be displayed in strong light.

Optical Properties

Color:

Scarlet, Vermilion or Reddish Gray

Transparency:

Translucent to Transparent (rarely); darkens with exposure to light

Luster:

Adamantine to Submetallic

Refractive Index:

2.792 - 3.088  Uniaxial ( - )

Birefringence:

0.295 - 0.296

Dispersion:

Very high

Pleochroism:

Moderate; cochineal-red to blood-red

Anisotrophism:

Strong

Occurances

Geological Setting:

A late-forming mineral in hydrothermal deposits, in the oxidized and enriched zone, associated with other silver minerals and sulfides.

Common Associations:

Silver, Arsenic, Xanthoconite, Stephanite, Acanthite, Tetrahedrite, Chlorargyrite

Common Impurities:

Sb

Type Locality:

Himmelsfurst mine, Erbisdor, near Freiberg, Germany

Year Discovered:

1832

View mineral photos:

Proustite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Proustite is a rare member of the Proustite Group of minerals that also includes Pyrargyrite. Both minerals are ofter referred to by the nickname "Ruby Silver" because of their deep red color and silver content. Proustite is a silver arsenic sulfide and Pyrargyrite is a silver antimony sulfide. The two are isostructural which means the two minerals have the same structure but a different chemistry. Proustite is rarer than Pyrargyrite espessially when it comes to faceted gems. Proustite gems are almost impossible to find since crystals are usually too small or dark and faceting is very difficult due to its softness. Proustite gems can be very attractive with the deep red color and adamantine luster.

Proustite, as with other silver minerals, is reactive to light and can form a white coating or turn black upon prolonged exposure. The white coating can be wiped off, but the blackening can't be reversed. Gems and specimens should be stored in the dark with limited light exposure.

Proustite occurs at many localities, but rarely in fine crystals or as an important ore mineral. From Germany, in the Himmelsfürst mine, Erbisdorf, near Freiberg; and at Niederschlema, Saxony. In Romania, at Sacarîmb (Nagyág). From Jáchymov (Joachimsthal) and Príbram, Czech Republic. At Sainte-Marie-aux-Mines, Haut-Rhin, France. From Sarrabus, Sardinia, Italy. In the USA, in Colorado, at Red Mountain, San Juan County, and at Georgetown, Clear Creek County; in Idaho, large masses at the Poorman mine, Silver City district, Owyhee County; in Nevada, in the Star mine, Cherry Creek district, White Pine County In Canada, from the Keeley mine, South Lorrain Township, Ontario. In Chile, at Chañarcillo, south of Copiapó, Atacama, as exceptional crystals. From Mexico, at Batopilas, Chihuahua, and Sombrerete, Zacatecas.
 

  
Proustite gems for sale:

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