Ultramafic Cumulate. Alaska.

This is a thin section of a ultramafic peridotite cumulate from the Brady Glacier Nunatak, La Perouse intrusion, Fairweather Range, S.E. Alaska USA. An exceptionally good cumulate texture, bright, colourless and totally fresh olivines in plagioclase and orthopyroxene poikilitic textured matrix. The orthopyroxene is in parts gradually altering to red/brown biotite, both parts in the same continuous crystal. Biotite is a hydrous mineral, so water must be present, but the olivine shows no sign of alteration. Highly Interesting.

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