Galena, niccolite, ullmannite, millerite, sphalerite and rammeslbergite. Settlingstones Mine, North Pennines, Britain

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Niccolite (pink-brown, bottom) crystals showing reflection pleochroism and bireflectance are altered along their edges and along fractures to rammelsbergite (white, higher reflectance, bottom left). Euhedral ullmannite crystals (light blue-white, high reflectance, centre top right) surround niccolite and are enclosed within galena (blue-white, lower reflectance, top). Minor amounts of millerite (yellow, bottom left) are associated with sphalerite (light grey, bottom left). A single sphalerite crystal lies beneath ullmannite, within galena (centre right). Black areas are polishing pits.

Polished block, plane polarized light, x 160, oil

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