Slate occurs as fine-grained, homogenous, sedimentary rock composed of clay or volcanic ash which has been metamorphosed (foliated) inside shells (bedded deposits). Slate may be mass produced into roofing slates (sometimes known as 'roofing shingles' in the United States), because it has two lines of fragility: cleavage & grain. This makes it conceivable to split slate into thinly sheets. Ticket slate can besides exist as utilized to hone knives.

Slate is in the main composed of quartz and muscovite (a mica), often along by owning biotite, chlorite, and hematite, or, less often, apatite, graphite, kaolin, magnetite, tourmaline, or zircon.

Occasionally of the finest slates in the globe are from either Portugal, Wales in the United Kingdom, the east coast of Newfoundland, and a "Slate Valley" of Vermont and New York.