ACANTHITE

Acanthite is a silver sulfide mineral represented by the chemical formula Ag2S. It crystallizes in the monoclinic system and remains stable as silver sulfide at temperatures below 173 °C (343 °F), while argentite is stable at higher temperatures. When argentite cools past this threshold, its cubic structure transforms into the monoclinic structure of acanthite, which can also form directly at temperatures below 173 °C. Acanthite is the only stable form of silver sulfide at typical ambient temperatures.

This mineral is frequently found in moderately low-temperature hydrothermal veins and areas of supergene enrichment, often occurring alongside native silver, pyrargyrite, proustite, polybasite, stephanite, aguilarite, galena, chalcopyrite, sphalerite, calcite, and quartz. Acanthite was first identified in 1855 in the Jáchymov district of the Ore Mountains, now part of the Karlovy Vary Region in the Czech Republic. Its name derives from the Greek word "akantha," meaning thorn or arrow, which reflects its distinctive crystal shape.

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