This is a strikingly orderly cluster of well-defined acanthite crystals (pseudomorphs after argentite) in parallel growth. The specimen is a floater. With magnification, one can see wires of silver protruding into gaps and hollows on the piece (these silver wires appear at least partially-pseudomorphed by a second generation of acanthite). Super acanthite.
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About These Acanthites
Well-crystallized acanthite has never been common and most of the known localities for crystals are historic, making it difficult, and usually expensive, to obtain fine specimens. The finds at Imiter (Africa’s largest silver mine) in recent years have placed it among the world’s best localities for crystallized acanthite. Although these crystals formed as argentite, argentite is not stable below 179C, at which point it changes to monoclinic acanthite. The specimens are acanthite pseudomorphs after argentite, retaining the isometric crystal form of the original argentite crystals. I assembled this lot of acanthites over a period of about two years. Most of these specimens, from the 2008 find, remained in Morocco until 2013.