Pyrite and marcasite. Galapagos Mound, Pacific Ocean

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Radiating aggregates of poorly crystalline pyrite (browner, lower reflectance, centre) form cores to euhedral or subhedral pyrite (yellow-white, centre right) which is intergrown with minor marcasite (blue-white, higher reflectance, top centre) in voids.

Polished block, plane polarized light, x 80, air

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