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aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.
..... Click the link for more information. formed when sedimentary rocks such as shaleshale,
sedimentary rock formed by the consolidation of mud or clay, having the property of splitting into thin layers parallel to its bedding planes. Shale tends to be fissile, i.e., it tends to split along planar surfaces between the layers of stratified rock.
..... Click the link for more information. are metamorphosed by great pressure. Slate splits into perfectly cleaved, broad thin layers; this characteristically regular and planar cleavage is called slaty cleavage. In the formation of slate, pressure causes the flaky minerals within the sedimentary rock, such as mica, clay, and chlorite, to be reoriented; the flat faces of the minerals lie at right angles to the source of the pressure, and the planes of easy cleavage are also at right angles to the source of the pressure. The rock is not necessarily compressed in the same direction as the sedimentary layers were originally laid down, and because the compression crumples and deforms the original sedimentary layers, the planes of slaty cleavage usually cut through the old bedding planes. Slate is intermediate in hardness between mica schistsschist
, metamorphic rock having a foliated, or plated, structure called schistosity in which the component flaky minerals are visible to the naked eye. Schists are distinguished from the other foliated rocks, slates and gneisses, by the size of their mineral crystals; these are
..... Click the link for more information. and shale; the better grades are used for roofing. Its characteristic color is gray-blue. Slate is mined in Maine, Vermont, Pennsylvania, Georgia, Lake Superior, and the Rocky Mts.
a schistous, sedimentary rock used for roofing. It consists of argillaceous minerals (for the most part, various hydromicas and chlorite) whose particles are usually arranged in strictly parallel lines. This structure gives slate a sharply defined schistosity, that is, the capacity for cleavage into thin lamina. Slate does not fall apart in water and has the characteristics of geosynclinal sediments. It is formed by the compaction of clays and their partial recrystallization under pressure at considerable depths as well as by the effect of dynamic metamorphism. When it undergoes further change, it becomes a phyllte or a chlorite slate.
The largest known deposits of slate in the USSR are located in the Caucasus and the Urals. Slate is used as roofing material; in the production of low-voltage switchboards, knife switches, and other apparatus in the electrical industry; and in the production of certain structural components (panels for the interior facing of rooms). Slate is also used in a crushed, roasted, and aerated form as filler for certain types of concrete, large wall blocks, and for cladding ruberoid(roof-sheeting material).
V. P. PETROV