Slate is a fine-grained, layered rock formed from sedimentary rock composed of clay or volcanic ash. It is formed by heat and pressure being applied to shale-like rock. 

Size - Ranges from 1/4" to 1/2".

Typical Uses - Pathway and landscape bed groundcover.

Coverage - 162 sf per cubic yard at 2" deep or 108 sf per cubic yard at 3" deep.