Magmatic sulphides
Chalcopyrite, pyrrhotite, pentlandite, and cubanite. Stillwater, Montana, USA
Pentlandite (light brown, high reflectance, centre top) has well developed (111) cleavage and flame-like margins (top, centre) growing into pyrrhotite. It is surrounded by an intergrowth of chalcopyrite (yellow, top left) and cubanite, which shows reflection pleochroism from light red-brown (centre right) to lilac-grey (centre). Pyrrhotite (dark brown, top left, top and bottom centre) surrounds pentlandite and shows cleavage. Silicates are black.
Polished block, plane polarized light, x 160. oil
Chalcopyrite, pyrrhotite, pentlandite and cubanite. Stillwater, Montana, USA
Chalcopyrite (yellow, bottom right) has thin cubanite exsolution lamellae (lilac-grey, bottom centre, top right) within it. Pentlandite flames (cream-white, high reflectance, centre) are intergrown with pyrrhotite (dark brown, top left). Cubanite (bottom left) shows reflection pleochroism from red-brown (very similar to pyrrhotite) to lilac-grey and is intergrown with chalcopyrite. Black areas are silicates.
Polished block, plane polarized light, x 160. oil
Chalcopyrite, pyrrhotite, cubanite and pentlandite. Stillwater. Montana, USA
Pyrrhotite (dark brown, top right) has a well developed cleavage which extends into chalcopyrite (yellow, top centre and left) and cubanite (blue-grey, centre right) areas, suggesting that chalcopyrite and cubanite are replacing pyrrhotite. Dark brown areas within chalcopyrite are relict pyrrhotite (bottom left). Pentlandite (pale brown-white, bottom) forms flames which are parallel with the basal (0001) cleavage of pyrrhotite. Silicates are black.
Polished block, plane polarized light, x 160, oil
Pyrrhotite, magnetite, pentlandite and chalcopyrite. Strathcona Mine, Sudbury, Ontario, Canada
Pyrrhotite crystals (light brown) have granular pentlandite crystals (light brown, higher reflectance, centre left) along their grain boundaries but are free of flame-like exsolution bodies of pentlandite. Magnetite (grey, bottom left) encloses a crystal of chalcopyrite (yellow, bottom left). Black areas are polishing pits.
Polished block, plane polarized light, x80, air
Pyrrhotite, pentlandite and chalcopyrite. Stillwater, Montana, USA
Pyrrhotite (brown) has pentlandite (light brown, higher reflectance, centre) exsolution bodies as flames, aligned along (0001). Minor amounts of chalcopyrite (yellow, centre right) are associated with cleavage and fractures within pyrrhotite. Silicates are black.
Polished block, plane polarized light, x 160, oil
Rhomb-shaped areas of deeply etched hexagonal pyrrhotite (lower 'reflectance, mottled brown-grey, centre and top right) are surrounded by more lightly etched monoclinic pyrrhotite, which is the main phase. Very lightly etched monoclinic pyrrhotite (pale brown, bottom right) has a rim of granular pentlandite (light brown, higher reflectance, bottom right). Pyrrhotite is intergrown with chalcopyrite (yellow, centre) and encloses subhedral magnetite (grey, top left), some of which is lightly etched (left bottom).
Polished block. etched with HI (hydriodic acid), plane polarized light, x80, air