Bornite, chalcopyrite and valleriite. Palabora, Republic of South Africa

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Bornite (pink-brown, top) is replaced by chalcopyrite (yellow, centre right) along (100). Valleriite (golden yellow, centre top and blue-green anisotropy colours, top centre) forms an incomplete rim around the copper-iron sulphides. The gangue is trigonal carbonate and shows curved deformation twins (centre top) and very faint internal reflections. Both valleriite and trigonal carbonates are strongly anisotropic, although the anisotropy of carbonates is often masked by their strong internal reflections.

Polished block, plane polarized light, x 160, air

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