Pyrrhotite, pyrite and marcasite. Nigadoo River, New Brunswick, Canada

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Coarse-grained pyrrhotite (browns) comprises higher reflectance monoclinic pyrrhotite along (0001) within lower reflectance, darker brown hexagonal pyrrhotite margins (centre right). It has altered to pyrite (light yellow), much of which is euhedral (top left), and to laths of marcasite (light blue-white, higher reflectance than pyrite, top right). The alteration can be seen to be crystallographically controlled along the basal cleavage of pyrrhotite. Black areas are silicates showing faint internal reflections (bottom left), -accessory minerals are dark grey (top centre).

Polished block, plane polarized light, x 180, oil

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