Acanthite is a form of silver sulfide with the chemical formula Ag2S. It crystallizes in the monoclinic system and is the stable form of silver sulfide below . 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 normal air temperature.
via Wikipedia infobox
{{infobox mineral | name = Acanthite | category = Sulfide mineral | boxwidth = | boxbgcolor = | image = Acanthite - Imiter mine, Jbel Saghro, Tinghir, Drâa-Tafilalet, Morocco.jpg | imagesize = 280px | alt = | caption = Crystallized acanthite (4.0 × 2.5 × 1.5 cm) from Imiter mine, Jbel Saghro mountain range, Morocco | formula = Ag2S |IMAsymbol=Aca | molweight = | strunz = 2.BA.30a | dana = | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/n | unit cell = a = 4.229 Å, b = 6.931 Å c = 7.862 Å; β = 99.61°; Z = 4 | color = Iron-black | colour = | habit = Primary crystals rare, prismatic to long prismatic, elongated along [001], may be tubular; massive. Commonly paramorphic after the cubic high-temperature phase ("argentite"), of original cubic or octahedral habit | twinning = Polysynthetic on {111}, may be very complex due to inversion; contact on {101} | cleavage = Indistinct | fracture = Uneven | tenacity = Sectile | mohs = 2.0–2.5 | luster = Metallic | streak = Black | diaphaneity = Opaque | gravity = 7.20–7.22 | density = | polish = | opticalprop = | refractive = | birefringence = | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }} Acanthite is a form of silver sulfide with the chemical formula Ag2S. It crystallizes in the monoclinic system and is the stable form of silver sulfide below . 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 normal air temperature.
==Occurrence== Acanthite is a common silver mineral in moderately low-temperature hydrothermal veins and in zones of supergene enrichment. It occurs in association with native silver, pyrargyrite, proustite, polybasite, stephanite, aguilarite, galena, chalcopyrite, sphalerite, calcite and quartz.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).