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Acanthite - Sold

Acanthite is a silver sulfide mineral. When crystallizing at a temperature above 176°C, the mineral has cubic symmetry. On cooling however, the symmetry changes to monoclinic (Petruk et al. 1974). This process is known as paramorphism, and such specimens are labeled "acanthite after argentite". Kenngott (1855) found some monoclinic crystals (formed below 176°C) and named this low temperature after the Greek for thorns, denoting its habit which is quite distinct from that of cubic argentite. This is nice example, consisting of stacked cubic crystals, each 3-4 mm across, forming a dense dendrite. This specimen was part of the personal collection of Ralph Merrill, proprietor of the prolific mail order business Minerals Unlimited, obtained in 1956. Merrill's collection card and label also ship with the specimen.