Argentopyrite, rammelsbergite, pyrargyrite, safflorite and violarite. Tynebottom Mine, North Pennines, Britain

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Argentopyrite (brown, top) shows faint reflection pleochroism from light to darker brown and is associated with pyrargyrite (blue, centre left) and an aggregate of violarite (pink-white, high reflectance, centre top) crystals. Locally, argentopyrite is extensively altered to pyrite, marcasite and AgFe8S11,, aggregates (centre right, bottom left). A veinlet of rammelsbergite (pink-white to blue-white, bottom left) shows high reflectance and faint reflection pleochroism; it is overgrown by rhombic safflorite (indistinguishable from rammelsbergite in plane polars at this magnification). The gangue is carbonate (light grey, bottom left) and quartz (darker grey, bottom centre).

Polished block, plane polarized light, x 80, air

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