Metapyroxenite (Shetland Ophiolite Complex, ~425-500 Ma; Skeo Taing, Balta Sound, Unst, Shetland Islands, North Sea)
Metapyroxenite (8.0 cm across) composed of chromian diopside pyroxene ((Ca,Cr)MgSi2O6 - calcium chromium magnesium silicate). Because this pyroxenite (a clinopyroxenite, really) is all diopside, a better rock name is diopsidite.
This is from an ophiolite complex (Shetland Ophiolite Complex; a.k.a. Unst Ophiolite Complex) exposed on the island of Unst in the northeastern Shetland Islands (in the North Sea, between Scotland & Norway). The rocks in the area represent ~basal crustal rocks metamorphosed during the Caledonian Orogeny (~425-500 million years ago). Published research indicates that the original rocks were from a late Neoproterozoic-Cambrian intracontinental, ocean-floored rift basin.
This metapyroxenite is from the upper pyroxenite layer of the Unst Ophiolite Complex.
Locality: outcrop at Skeo Taing, shores of Balta Sound, eastern margin of island of Unst, northeastern Shetland Islands, North Sea
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Ophiolites are fragments of oceanic lithosphere (basaltic crust + uppermost mantle) that have been metamorphosed and plastered onto the edges of continental lithospheric plates by obduction (the opposite of subduction).