Photomicrograph of garnet in crossed polarized light. The dark layers are nearly pure andradite (calcium-iron garnet), whereas the light layers also contain varying amounts of grossular (calcium-aluminum garnet). This sample is from the metamorphic aureole of the Drammen granite in the Permian Oslo Rift. Analysis of the garnet provides information on the evolution of the hydrothermal system during metamorphism. (Field width is 3.2 mm.) See page 505. [Photomicrograph: Bjørn Jamtveit]

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