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#xenolith

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#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

Rock on the beach at Barnum Point, Camano Island, WA. Looks like a granodiorite peppered with xenoliths. Igneous petrologists chime in. Likely weathered out of the till that caps the bluffs or a dropstone from floating ice on marine water incursion during the Everson interstade. Source rock provenance not known. Ref. Geologic map of the Juniper Beach 7.5-minute quadrangle, WDGER Geologic Map GM70.

X is for Xenolith (and Xenocryst)

“A xenolith ("foreign rock") is a rock fragment (country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock entrained during magma ascent, emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing body of lava on the Earth's surface. A xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes.”
~ From Wikipedia

See more: blogs.agu.org/georneys/2011/05