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Migmatite is a composite rock found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock that was reconstituted subsequently by partial melting ("paleosome"), while the alternate layer has a ...
Ptygmatic (folding); see migmatite; Q. Quench textures; see obsidian, tachylyte or aphanitic; R ... This section is empty. You can help by adding to it. (March 2013) V
A cross-polarized thin section image of a garnet-mica-schist from Salangen Municipality, Norway showing the strong strain fabric of schists. The black crystal is garnet, the pink-orange-yellow colored strands are muscovite mica, and the brown crystals are biotite mica.
A slate is a fine-grained metamorphic rock that easily splits into thin plates but shows no obvious compositional layering. The term is used only when very little else is known about the rock that would allow a more definite classification.
Migmatite is a gneiss consisting of two or more distinct rock types, one of which has the appearance of an ordinary gneiss (the mesosome), and another of which has the appearance of an intrusive rock such pegmatite, aplite, or granite (the leucosome). The rock may also contain a melanosome of mafic rock complementary to the leucosome. [11]
Thin section image of a foliated cataclasite in both plane polarized light (right) and crossed polarized light (left). The banding in this cataclasite is defined by grain size and ratio of clasts to matrix. This rock is from the San Andreas Fault at Elizabeth Lake, California.
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For example, in thin section examination, biotite crystal is included in a garnet grain, so biotite is considered to be formed at an earlier time. Peak metamorphism. Porphyroblastic-matrix texture: [18] large euhedral crystals inside a fine groundmass. Both the euhedral crystals and the matrix minerals of the porphyroblasts are formed at peak ...