#ThinSectionThursday A complex bit of Earth's mantle brought to the surface by a kimberlite (strictly, an orangeite) from Finsch mine, South Africa. The stand-out clear (black) grain is pyrope garnet. Most of the clear (bright coloured) grains are olivine. The pale brown (rainbow) rim around the pyrope is phlogopite mica, formed by a process called metasomatism. These rocks contain diamonds, but none visible here! See ALT text for more info... #Geology #Mantle #Xenolith #Diamond #Microscopy