slate

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slate,

fine-grained rockrock,
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.
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 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.
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 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
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 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.

slate

A hard, brittle metamorphic rock characterized by good cleavage along parallel planes; used as cut stone in thin sheets for flooring, roofing, and panels, and in granular form as surfacing on composition roofing.
See also: Stone

Slate

 

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

slate

[slāt]
(petrology)
A group name for various very-fine-grained rocks derived from mudstone, siltstone, and other clayey sediment as a result of low-degree regional metamorphism; characterized by perfect fissility or slaty cleavage which is a regular or perfect planar schistosity.

slate

A hard, brittle metamorphic rock consisting mainly of clay minerals, characterized by good cleavage along parallel planes; used extensively as dimension stone in thin sheets for flooring, roofing, panels (both decorative and electrical), and chalkboard, and in granular form as surfacing on composition roofing.

slate

1. 
a. a compact fine-grained metamorphic rock formed by the effects of heat and pressure on shale. It can be split into thin layers along natural cleavage planes and is used as a roofing and paving material
b. (as modifier): a slate tile
2. a dark grey colour, often with a purplish or bluish tinge
3. Chiefly US and Canadian a list of candidates in an election
4. Films
a. the reference information written on a clapperboard
b. Informal the clapperboard itself

slate

Another name for a tablet computer. In 2010, HP introduced tablets under the Slate brand. See Tablet PC and tablet computer.
References in periodicals archive ?
3m on a building to celebrate Scottish stone quarrying - then using Spanish slate for the roof.
PetraSlate offers slates that carry either class 3 or class 4 hail ratings, depending on the thickness of the slate purchased.
WELSH blue slate from North Wales is being used to re-roof the Old Town Hall in Merthyr Tydfil as part of its pounds 8m restoration.
HUGE slate pillars celebrating Blaenau Ffestiniog's historic and cultural roots are being put up this week as part of a major pounds 4.
There will be dozens of other slates announced, many overlapping, but they are not expected at this point to have much impact.
Disputes between the two slates go back to January 2009 when Hadba' Slate took over all of the provincial council's upper posts after having won 19 out of the Council's 37 seats, while Niniveh Fraternal Slate, headed by Khisro Koran, got only 12 seats forcing it to boycott the Council taking with it 16 administrative entities.
Slates vary hugely from area to area, but they're usually laid treble lapped.
In some markets the price difference between synthetics and natural slates may be 10% to 15% or more per square; in other markets it may be only a few dollars, up or down.
High-ranking officials of Sierra Canyon School are among candidates being promoted on a slate that, in an election to be held Saturday, could become a new majority on the Chatsworth Neighborhood Council.
Aesthetically, however, the British home buyer has preferred the pitched roof finished in slates or tiles.
Slate is the Robert Redford of the stone world: Its rugged good looks and versatility allow it to play a wide range of roles; its mood can be rustic and casual or sleek and contemporary.
Those of us who come from Africa remember that in school we used to have slates, and had to wipe them clean several times a day.