Pyrite, niccolite, vaesite, rammelsbergite and marcasite. Settlingstones Mine, North Pennines, Britain

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Niccolite (pink, bottom) shows faint reflection pleochroism and bireflectance. It is altered along grain edges and along fractures to rammelsbergite (blue-white, centre bottom) accompanied by vaesite (violet-brown with cleavage, centre, top right). A central vein of coarse-grained pyrite (yellow-white) is intergrown with marcasite (green-blue, centre). Black areas are gangue minerals.

Polished block, plane polarized light, x 160, oil

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