Nickeliferous marcasite and bravoite. Oxclose Mine, South Pennines, Britain

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Euhedral, zoned bravoites have lower reflectance than the enclosing zoned marcasite. Bravoite shows higher reflectance cores and lower reflectance outer zones and has a pentagonal dodecahedral habit (centre left). The enclosing marcasite is coarse-grained and also shows faint nickel-rich zoning (centre). Nickel-poor marcasite is unzoned, has a slightly higher reflectance, and occurs on the margin of the nickeliferous marcasite (bottom right). Different crystals show reflection pleochroism (green-blue to yellow, bottom centre).

Polished block, plane polarized light, x 400, oil

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