Chromite, pentlandite, heazlewoodite, millerite and ferritchromit. Unst, Shetland Islands, Britain
Chromite (dark grey, top left) has a thin spongy ferritchromit rim (lighter grey). Pentlandite (brown, centre) shows good cleavage along (111) and has altered, partially along this cleavage, to heazlewoodite (white, higher reflectance, centre bottom) which in turn has altered to millerite (yellow-white, lower reflectance, bottom centre left) with a trellis-like parting/cleavage. Black areas are silicates.
Polished block, plane polarized light, x 160, oil