pyrargyrite

(pī-rär'jə-rīt', pĭ-)
n.
A deep red to black silver ore with composition Ag₃SbS₃.

[German Pyrargyrit : Greek puro-, pyro- + Greek arguros, silver; see argent.]

A mineral having composition Ag₃SbS₃. The mineral occurs as prismatic crystals and in massive form and in disseminated grains. The hardness is 2.5 on Mohs scale and specific gravity is 5.85. The luster is adamantine and the color a deep ruby red to black, giving it the name dark ruby silver. Pyrargyrite is an important silver ore when it is found in veins associated with proustite and other silver minerals. It has been mined as silver ore at Chanarcillo, Chile; Freiberg, Germany; Guanajuato, Mexico; and Cobalt, Ontario, Canada. See also Proustite.

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Ag
Hexagonal -- Ditrigonal pyramidal

Environment

Low-temperature silver veins.

Crystal description

Often well crystallized; being hemimorphic, the upper faces differ from those of the lower end, although since crystals are seldom doubly terminated, this phenomenon is not usually apparent. Most often truncated at the tip with gently sloping rhombohedron faces above steep scalenohedrons. Also massive.

Physical properties

Deep red to almost black. Luster adamantine; hardness 2Ɖ; specific gravity 5.8-5.9; streak purplish red; fracture conchoidal; cleavage 2 rhombohedral (1 good). Brittle.

Composition

Silver antimony sulfide (59.9% Ag, 22.3% Sb, 17.8% S). Surprisingly low arsenic substitution for antimony, even though it often occurs with proustite.

Tests

Fuses readily into round shiny globule. Antimony sublimate forms white ring close to assay, best seen immediately after first melting. Continued heating creates a dull gray malleable button, which gives good test for silver (hydrochloric acid added to nitric acid solution).

Distinguishing characteristics

Usually the crystal form and dark red color are a sufficient guide. Pyrargyrite could be confused with dark proustite, but the antimony sublimate around the pyrargyrite button reveals a difference. Cuprite gives copper tests; zincite is infusible. In general, the mineral associations suggest silver minerals whenever we encounter pyrargyrite or proustite.

Occurrence

Pyrargyrite is a late mineral in the silver veins, and probably is also formed secondarily by hot volatile compounds reworking earlier deposits. Specimens are usually discovered only in the early stages of a silver-mining operation, when it is sometimes an important ore of silver. Although fine specimens are often destroyed to quickly obtain their silver value, the specimen value of good crystals is, as a rule, far greater. The best examples have come from Germany, in the Harz and Saxony. In France good crystals were found at Sainte-Marie-aux-Mines, Alsace, and at Chalanches, Isère. Chanarcillo, Chile, better known for its proustite, was a great source, as was Colquechaca, Bolivia. Some Mexican mines, as at Guanajuato, have enough pyrargyrite for it to be an ore. It is not abundant in the U.S. Castrovirreyna, Peru, has lately been a source of respectable examples.

Remarks

Known as dark ruby-silver ore (dunkles Rotgültigerz) , distinguished as a rule by its deeper hue from the light ruby-silver ore, proustite (lichtes Rotgültigerz) . Both, on exposure to light, have a tendency to darken and develop a dull coating that dims their luster. If the specimen is sturdy enough to stand it, a light brushing with soap and water will remove much of the coating. A quick dip in a silver-polishing solution has been found effective but may be risky to the luster.

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