Leisteen

Leisteen is the Dutch term for slate, a fine-grained metamorphic rock formed from shale or mudstone under low-grade regional metamorphism. Slate is distinguished by its foliated texture and slaty cleavage, which allows it to split readily into thin, durable sheets along planes of weakness. The mineral composition typically includes quartz, micas (such as muscovite or biotite), chlorite, and minor iron oxides, giving colors that range from gray and blue-gray to green or purple.

Formation and properties: Slate forms when shale or pelite is subjected to burial and directed pressure, causing the platy minerals to align perpendicular to the stress direction. This foliated structure yields flat, smooth surfaces and the ability to fracture into flat slabs, a feature known as cleavage. Slate is relatively dense and offers moderate hardness, making it resistant to weathering in many climates.

Distribution and uses: Slate occurs in various regions worldwide, with historic quarry belts in Europe and continued production in many countries. It is widely used for roofing tiles, floor and wall tiles, paving, and as a bed material for billiard tables. Slate’s durability and clean cleavage also made it a traditional material for chalkboards and laboratory surfaces, though modern boards have largely replaced some uses.

See also: Slate, metamorphic rock.