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Gneiss Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks. Gneissic rocks are usually medium- to coarse-foliated and largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, etc. Depending on their composition, they may also be called garnet gneiss, biotite gneiss, albite gneiss, etc. (source: Wikipedia) Photo by Michael Marcotte Photo by Sim Sepp Photo by Eurico Zimbres Return to List Back to Michael's Hobbies page Back to Michael Marcotte's HomePage