Home > Silver and Gold Minerals – January 7 > MS1473 Acanthite on Polybasite

Acanthite on Polybasite


Acanthite is a silver sulfide mineral. At temperatures in excess of 176°C, silver sulfide crystallizes with cubic symmetry. On cooling however, the symmetry changes to monoclinic (Petruk et al. 1974). This reversible symmetry change is called paramorphism, and specimens like this example may be labeled "acanthite paramorph after argentite". Kenngott (1855) found some monoclinic crystals of acanthite (formed below 176°C) and named the low temperature form of silver sulfide after the Greek for thorns, denoting its habit which is quite distinct from that of cubic argentite.

This is a mass of paramorphous acanthite crystals to 5 mm formed on a thick polybasite crystal. The polybasite crystals here are incomplete, but Arizpe is known to have produced some of the largest crystals known. This is an old specimen, the crystals are somewhat rounded from drawer wear. Such specimens date to a mining period before World War I.

Price: $175

Item code: MS1473

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