Slate is a fine grained metamorphic rock formed from clay, sedimentary rock shale, and sometimes quartz. Slate is a hard stone but brittle which will break easy into smooth slabs. The availability of slate in various colors including gray, black, brown, green, red, or purple makes it further suitable for commercial use such as blackboards, flagstone, and roofing tiles. Generally, tabletops for the best pool tables are made of slate.