Slate

slate, a moderately hard, very fine-grained metamorphic rock (see geology), the result of the burial of pre-existing rocks such as mudstone, shale, and volcanic tuff, with a marked propensity to cleave into thin sheets. With increased metamorphism, slate becomes schist.

Slate is found, for example, in the Cederberg Mountains, south africa, and the clare valley, South Australia. It is particularly celebrated in Germany’s mosel and rhine regions, where it makes famously stony slopes and is thought to hold moisture and heat and radiate warmth at night.