Chalcopyrite, sphalerite, pyrite and marcasite. Jersey, Channel Islands, Britain

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Chalcopyrite (yellow, bottom left) encloses small sphalerite stars (grey), whereas sphalerite (light grey, bottom right) has chalcopyrite inclusions (yellow), many of which are crystallographically oriented; this is chalcopyrite disease. Lath-shaped intergrowths of pyrite (light yellow-white, centre top) and marcasite (blue-green white, slightly higher reflectance) are pseudomorphs after pyrrhotite crystals. It is difficult to distinguish between the disulphides at this magnification. The low reflectance rounded area (centre bottom) within chalcopyrite is a limonite pseudomorph after pyrrhotite. Rhombic carbonate (dark grey, top right) shows faint bireflectance and internal reflections. Black areas are polishing pits.

Polished block, plane polarized light, x 80, air

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