Slate is the finest grained of the metamorphic rocks. Characteristics such as strength, color, density and absorbency vary by geographic location because of varying geologic forces, like heat and pressure, imposed upon it at the time of formation.
Slate is morphed from shale, a sedimentary rock with high clay content. Slate also contains varying degrees of chlorite, kaolinite, micas and quartz, among other minerals. Colors vary but are characteristically grayish blue.
The majority of slate is considered a soft rock; you can scratch it easily.
Slate cleavage appears as paper-thin, extremely strong planes that are oriented at right angles to the source of imposed pressure.
Slate generally has a low rate of absorption, but slate with a high content of a type of clay called kaolinite will absorb liquid at a faster rate.
Slate’s qualities make it a good choice for roofing, flooring, tombstones and as landscaping and garden decor because it is more durable than synthetic materials.