Slate
Roofing slates are commonly split so that the length of the slate runs in the direction of the natural grain. The surface texture of slate, after it is split for commercial use, depends on the quality and the characteristics of the rock from which it was quarried. Some slate contains narrow "ribbons of rock" that are different in chemical composition and color from the principal slate. Slate that has been trimmed so that the ribbons are eliminated is known as clear slate. Slate that contains acceptable ribbons is sold as ribbon stock.
 

Manufactuers

		http://www.echeguren.com
		http://www.truslate.com
		http://www.ncslate.com
		http://www.evergreenslate.com