Slate

n. [O. Eng. sclate, sclat; O. Fr. esclat, N. Fr. éclat, a shiver, splinter, esclater, éclater, to shiver, to chip, Pr. esclatar, from O. H. Ger. steizan, for skleizan, N. H. Ger. schleizen, to slit, split. Cf. Ir. sglata, Gael. sgliat, a slate, a tile.]

1. (Min.) An argillaceous stone which readily splits into plates; argillite; argillaceous schist.
2. Any rock or stone having a slaty structure.
3. A prepared piece of such stone; especially, (a.) A thin, flat piece, for roofing or covering houses, &c. (b.) A tablet for writing upon.
4. An artificial material, resembling slate, and used for the above purposes.
5. A thin plate of any material; a flake. [Obs.]

Adhesive slate, a kind of slate of a greenish-gray color, which absorbs water rapidly, and adheres to the tongue; whence the name. Buchanan.—Aluminous slate, or alum slate, a kind of slate containing alumina, used in the manufacture of alum. It is found low down in the coal measures.—Argillaceous slate, clay-slate. See CLAY-SLATE.—Bituminous slate, a soft species of sectile slate-clay, impregnated with bitumen. Buchanan.—Drawing slate, a kind of soft chalk, of a black or bluish-black color and slaty fracture, containing some carbon, and used in crayon-drawing:—called also graphic slate and black chalk. Tomlinson. Buchanan.—Hone slate. See WHET-SLATE.—Hornblende slate, a slaty rock, consisting of hornblende and feldspar, with some chlorite,—useful, on account of its toughness, for flagging. Dana. Tomlinson.—Polishing slate, a silicious, slaty mineral, of a yellowish color, and very soft, found in Bohemia.—Slate clay, an indurated clay, forming one of the alternating beds of the coal measures, consisting of an infusible compound of alumina and silica, and often used for making fire-bricks. Tomlinson.—Slate globe, a globe the surface of which is made of an artificial slate-like material.—Slate rocks, rocks which split into thin lamina, which are not parallel to the stratification; foliated rocks.—Slate-spar, a variety of carbonate of lime of silvery-white luster, and of a slaty structure, or sometimes crystallized in thin intersecting plates.