Magmatic nickel ores
Pyrrhotite, pentlandite, pyrite and chalcopyrite. Kambalda, Western Australia
Coarse-grained pentlandite (yellow-brown, centre and right) shows characteristic cleavage along (111) and is intergrown with pyrrhotite (pink-brown, lower reflectance than pentlandite, left and bottom right). Pyrrhotite has rims of pyrite (white, centre bottom) and chalcopyrite (centre) which has tarnished to a dull yellow. Minor amounts of pyrite form areas within pyrrhotite along crystal boundaries (top left). Dark grey areas are silicates and black areas are polishing pits.
Polished block, plane polarized light, x 100. air
The central spinel phase is zoned with a lower reflectance core (light grey, centre) of chrome-rich spinel (ferrochromite) and a higher reflectance iron-rich rim (magnetite) (bottom centre). It is extensively shattered and the fractures are infilled with chalcopyrite. Chalcopyrite (yellow, left) is intergrown with pyrite (pale yellow-white, higher reflectance, right) and euhedral to subhedral highly altered pentlandite (light yellow brown, many polishing pits, top centre). Violarite (brown, top right) is the main alteration product of pentlandite. Dark grey areas are silicates.
Polished block, plane polarized light. x80, air
Pyrrhotite and pentlandite. Kambalda, Western Australia
Pyrrhotite (brown, centre) carries flame-like exsolution bodies of pentlandite (light brown, higher reflectance, centre right). Many of these exsolution bodies are associated with fractures in the pyrrhotite and are oriented along its (0001) plane. Black areas are silicates and polishing pits.
Polished block, plane polarized light. x 80, air
Altered pentlandite, pyrite, pyrrhotite, chalcopyrite and spinel. Kambaida, Western Australia
Central pyrrhotite (brown) and euhedral spinel (ferrochromite) (grey, centre left) are surrounded by extensively altered pentlandite (light brown, abundant fine polishing pits, top) crystals. The alteration of pentlandite to violarite lowers its reflectance and alters its surface colour from brown-yellow to red-brown. Pyrite (light yellow, high reflectance, left) is intergrown with chalcopyrite (yellow, bottom right) and surrounds altered pentlandite. Dark grey areas are silicates, black areas are polishing pits.
Polished block, plane polarized light, x80, air
Pyrite, chalcopyrite, spinel, altered pentlandite and native gold. Kambalda, Western Australia
Coarse-grained pyrite (light yellow-white, left) is intergrown and replaced by chalcopyrite (dull yellow, right). Euhedral to subhedral spinel crystals, (light grey, left centre) occur within pyrite and chalcopyrite. Native gold (golden yellow, very high reflectance, centre) makes the sulphides appear dull. Pentlandite (brown-pink, top left) is present but is extensively altered to violarite.
Polished block, plane polarized light, x80, air
Pentlandite, pyrite, chrome-rich spinel, magnetite and chalcopyrite. Kambalda, Western Australia
Pentlandite crystals (light brown, centre left) with cleavage along (111) are replaced by pyrite (light yellow, higher reflectance) and chalcopyrite (tarnished to dull yellow, centre). Zoned euhedral spinel crystals (bottom) comprise chrome-rich cores (ferrochromite) (light grey-green) and magnetite rims (brown-grey). A small chalcopyrite crystal (yellow, bottom) is untarnished and shows its true surface colour and reflectance. Silicates are dark grey.
Polished block. plane polarized light. x90, air