Slate

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

Slate ranges in color from gray to black or from red to green, depending on the minerals contained in the shale from which it formed.

Slate is incredibly durable: it can last up to several hundred years. As a natural resource, it offers many environmental benefits. Its low tendency to absorb water also makes it very resistant to frost damage and breakage due to freezing. Natural slate is also waterproof and fireproof resistant and energy efficient. It requires little or no maintenance.

Spain is the world's largest producer and exporter of natural slate. China has vast slate deposits in various colors. Slate is produced on the east coast of Newfoundland, in Eastern Pennsylvania, Buckingham County, Virginia, and the Slate Valley of Vermont and New York, where colored slate is mined in the Granville, New York area.

- Wikipedia (online April 2014)