Schist section photomicrograph cross polarized lighting mag approx X150
Schist is a metamorphic rock which means that it was formed by the transformation of other types of rock under conditions of great heat and pressure deep in the Earth s crust Metamorphic rocks come in a sequence of what are called metamorphic grades Rocks of low metamorphic grade such as slate are rocks in which the process of metamorphism has been halted at a relatively early stage and rocks of high metamorphic grade such as gneiss have been subjected to extensive metamorphism at very high pressures and at temperatures just short of being high enough to cause them to melt Schist is intermediate between slate and gneiss and is toward the higher end of metamorphic grade closer to gneiss than to slate Gneiss is widely used as an ornamental building stone because it takes a fine polish and can be quite beautiful All metamorphic rocks show an alignment of their crystals because the high pressure in which they were formed tends to cause crystals to grow in the same alignment With gneiss this alignment of the crystals can come out when polished as a lovely pattern of banding of the different minerals such as pink feldspars and glassy quartz Schist contains more mica than gneiss does and since mica is a flaky mineral it is hard to work with Schist would be more difficult to polish than gneiss and would tend to stand up less well to weathering if placed say on the outside of a building But still you might be able to find examples of schist used as a polished ornamental stone Another use for schist is that it is a source of the semi precious gemstone called garnet Garnet is a mineral that is nearly always found only in schists and there are many schists throughout the world in which large crystals of garnet can be found In the United Kingdom for example schists from Scotland are well known for their beautiful garnets Conglomerate is a sedimentary rock formed by the transportation and deposition of eroded fragments of other rocks by the action of running water as in rivers an
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Keywords: approx, architectural, birefringence, building, cross, facing, lighting, mag, materials, microscope, ornametal, photomicrograph, polarized, schist, section, stone, x150
