Slate roofing is a hard, durable rock material that is basically non-absorbent  and is used primarily on residential and commercial projects that have steep sloped roof areas.  

Slate roofing is quarried from the ground and split by hand.  The surface texture and color of slate is determined by the characteristics, chemical, and mineral composition of the rock from which it is  quarried.

Because these factors differ from quarry to quarry, slate is available in a variety of colors.  In addition, exposure to the weather causes slate to change color.  Slate that changes color is referred to as weathering or semiweathering.