Acanthite

Acanthite, Ag2S, crystallizes in the monoclinic system and is the stable form of silver sulfide below 173 °C. Argentite is the stable form above that temperature. As argentite cools below that temperature its cubic form is distorted to the monoclinic form of acanthite. Below 173 °C acanthite forms directly. Acanthite is the only stable form in n...
Found on http://en.wikipedia.org/wiki/Acanthite

acanthite

a silver sulfide mineral (Ag2S) that is the most important ore of silver. It is abundant, with other silver minerals, in the sulfide mineral deposits ...
Found on http://www.britannica.com/eb/a-z/a/9

Acanthite

Acanthite is a mineral very similar to argentite, differing only in internal structure; the crystal of Acanthite being monoclinic - acanthite can be turned into argentite by heating. Acanthite is an important ore of silver, and forms spiky-looking crystals.
Found on http://www.probertencyclopaedia.com/browse/HA.HTM

Acanthite

Ag2S An ore mineral of silver
Found on https://www.encyclo.co.uk/local/20501
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