ACANTHITE MINERAL FACTS Nevada Turquoise gem stones
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Acanthite Mineral Facts:

Chemical Formula: Ag2S (Previously known as Argentite) 87.1% Silver by weight

Colors: Mineral and streak are blackish to lead-gray. Streak sometimes has metallic shine.

Hardness: 2.0 to 2.5
Hardness varies somewhat depending on formation and impurities.

Density: 7.3
The density is high because of the large silver content. 

Cleavage: Imperfect, but  it is easily sectile, and can be cut with a knife like lead.

Crystallography: Monoclinic

Luster:. Metallic luster. Easily sectile, and can be cut with a knife like lead.

Optics: (Refractive Index):  Opaque

Acanthite crystals on calcite, Argentite

Composition, Structure and Associated Minerals:
Acanthite, though not very widespread in its occurrence, is an important silver ore. It is found in masses, as coatings, and in crystals  or arborescent groups of crystals.  Acanthite is usually, however, impure through the admixture of small quantities of Fe, Pb, Cu, etc.  It is most commonly found as massive, platy, earthy forms or as a coating on other rocks. Well formed crystals are fairly rare. The crystals are often distorted and grouped into parallel growths of different shapes. Twinning is common, with P(111) the twinning plane. The twins  are usually penetration twins. The habit of most crystals appears cubical because of twinning, but are actually monoclinic.

Identification and Diagnostics
Easily fusible at 1.5 with intumescence. When fused alone on charcoal in an open flame, it gives off odor of sulphur dioxide and yields a globule of pure silver. Distinguished by these tests and by its color, sectility and high specific gravity. It is soluble in nitric acid.

Occurrence, Localities and Origins:
A fairly common ore of silver. Usually found in silver veins as small masses, often earthy or as a coating. Associated with native silver, the ruby silvers, stephanite and other silver minerals as well as other sulfides such as galena. The mineral is found in the secondary  enrichment zones of veins associated with silver and other sulfides  in many silver-mining districts. In Nevada it is an important ore at  the Comstock lode, Tonopah and in the Cortez district. It is found also near Port Arthur on the north shore of Lake Superior, in Ontario, and associated  with native silver in the copper mines of Michigan. The rich silver ores of  Mexico, Chile, Bolivia and Peru are composed largely of this mineral. Important European localities for its occurrence are Freiberg in Saxony, Annaberg in Austria, Joachimsthal in Bohemia, Schemnitz and Kremnitz in Hungary and Kongsberg in Norway. Much of the silver produced in the US country was obtained from acanthite, though by no means so great a quantity as is obtained from other sources. Still, it is an important ore of silver.

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Acanthite, Earthy Form

Acanthite, Earthy Form

Acanthite (argentite) crystals



Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.

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