Search results
Results from the WOW.Com Content Network
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 ("neosome"), while the alternate layer has a ...
Main page; Contents; Current events; Random article; About Wikipedia; Contact us
In structural geology, ultramylonite is a kind of mylonite defined by modal percentage of matrix grains [clarify] more than 90%. [4] Ultramylonite is often hard, dark, cherty to flinty in appearance and sometimes resemble pseudotachylite and obsidian. In reverse, ultramylonite-like rocks are sometimes "deformed pseudotachylyte". [5] [6] [7] [8]
Thin sections are prepared in order to investigate the optical properties of the minerals in the rock. This work is a part of petrology and helps to reveal the origin and evolution of the parent rock. A photograph of a rock in thin section is often referred to as a photomicrograph.
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.
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.
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]
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 ...