Slate is a fine-grained homogeneous
sedimentary rock composed of
clay or
volcanic ash which has been
metamorphosed (foliated) so as to develop a high degree of fissility or slaty cleavage which is usually at a high angle to the planes of stratification. This high degree of fissility makes the better grades of slates an extremely useful
roofing material (although its use has fallen in favor of synthetic and manufactured substitutes). The finest slates in the world come from
Wales,
Britain.
See also: List of minerals
Slate is a news e-zine[?].
Slate is also a prototype based object-oriented programming language with multiple dispatch. It uses the syntax of Smalltalk and some ideas of Self, and is currently being developed at http://slate.tunes.org.