Chalcopyrite, pentlandite and altered pentlandite. Palabora, Republic of South Africa
Chalcopyrite (yellow) contains triangular-shaped inclusions of pentlandite (pale yellow, highest reflectance, centre bottom). Pentlandite has extensively altered, from its grain boundaries inwards, to a fine-grained mixture of violarite and bravoite (lower reflectance, pink-brown, centre bottom). At higher magnification the two secondary minerals can be distinguished from each other. Black areas are silicates.
Polished block, plane polarized light, x 160, oil