Proustite
Image: Parent Géry (Public domain)
Mineral NameProustite
Chemical FormulaAg3AsS3
Mohs Hardness2
Crystal Systemtrigonal
Lusteradamantine
Streak Colorred
Cleavage{1011} distinct
Fractureconchoidal
Specific Gravity5.57
Colorsruby-red, dark red, reddish-black
Transparencytranslucent
Type LocalityFreiberg, Saxony, Germany; Chañarcillo, Atacama, Chile
Mineral GroupSulfosalts
Usescollector, minor silver ore
Associated Mineralssilver, pyrargyrite, galena, sphalerite, calcite, rhodochrosite
Rarityuncommon
Description
This specimen features several dark ruby-red to reddish-black proustite crystals with a brilliant adamantine luster, perched on a matrix of lighter pinkish-white mineral, likely rhodochrosite or calcite, and a darker host rock.
Geological Context
Proustite is a low-temperature hydrothermal mineral found in silver-rich veins, typically forming in the upper oxidized zones of ore deposits. It often occurs with other silver sulfosalts and native silver.
