Proustite

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Proustite
Proustite-209739.jpg
General
CategorySulfosalt minerals
Formula
(repeating unit)
Ag3AsS3
Strunz classification2.GA.05
Neso-sulfarsenites
Dana classification03.04.01.01
Proustite group
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M Symbol: (3 2/m)
Space groupR3c
Unit cella = 10.79 Å, c = 8.69 Å; Z = 6
Identification
ColorScarlet-vermilion
Crystal habitCrystals prismatic and scalenohedral, massive, compact
TwinningCommon
CleavageDistinct on {1011}
FractureConchoidal to uneven
TenacityBrittle
Mohs scale hardness2 – 2.5
LusterAdamantine
StreakVermilion
DiaphaneityTranslucent, darkens when exposed to light
Specific gravity5.57 measured, 5.625 calculated
Optical propertiesUniaxial (-)
Refractive indexnω = 3.087 - 3.088 nε = 2.792
Birefringenceδ = 0.295 - 0.296
PleochroismModerate; cochineal-red to blood-red
References[1][2][3]

Proustite is a sulfosalt mineral consisting of silver sulfarsenide, Ag3AsS3, known also as light red silver or ruby silver ore, and an important source of the metal. It is closely allied to the corresponding sulfantimonide, pyrargyrite, from which it was distinguished by the chemical analyses of Joseph L. Proust (1754–1826) in 1804, after whom the mineral received its name.

The prismatic crystals are often terminated by the scalenohedron and the obtuse rhombohedron, thus resembling calcite (dog-tooth-spar) in habit. The color is scarlet-vermilion and the luster adamantine; crystals are transparent and very brilliant, but on exposure to light they soon become dull black and opaque. The streak is scarlet, the hardness 2 to 2.5,[4] and the specific gravity 5.57. Its transparency differs from specimen to specimen, but most are opaque or translucent.[5]

Proustite occurs in hydrothermal deposits as a phase in the oxidized and supergene zone. It is associated with other silver minerals and sulfides such as native silver, native arsenic, xanthoconite, stephanite, acanthite, tetrahedrite and chlorargyrite.[1]

Magnificent groups of large crystals have been found at Chañarcillo in Chile; other localities which have yielded fine specimens are Freiberg and Marienberg in Saxony, Joachimsthal in Bohemia and Sainte-Marie-aux-Mines in Alsace[citation needed].

Structure[edit]

Subunit of the proustite structure, showing the connectivity of Ag, As (violet), S.
The structure of proustite can be viewed as the Ag+ derivative of [AsS3]3−.[6]

See also[edit]

References[edit]

  1. ^ a b http://rruff.geo.arizona.edu/doclib/hom/proustite.pdf Handbook of Mineralogy
  2. ^ http://www.mindat.org/min-3294.html Mindat.org
  3. ^ http://www.webmineral.com/data/Proustite.shtml Webmineral
  4. ^ "Proustite". www.mindat.org. Retrieved 2021-08-12.
  5. ^ "Proustite Value, Price, and Jewelry Information". International Gem Society. Retrieved 2021-08-12.
  6. ^ Engel, P.; Nowacki, W."Die Verfeinerung der Kristallstruktur von Proustit, Ag3As S3 und Pyrargyrit, Ag3SbS3" Neues Jahrbuch fuer Mineralogie. Monatshefte 1966, p181-p184

 This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Proustite". Encyclopædia Britannica. 22 (11th ed.). Cambridge University Press. p. 490.