skifer

Skifer is a fine-grained sedimentary rock that forms from the compaction of silt and clay in calm water settings. The name derives from its fissility, the tendency to split readily along thin layers parallel to bedding. Typical shales are gray to black, greenish, or reddish, and often contain fossils or organic material that can darken the rock.

Chemically, skifer consists mainly of clay minerals such as illite and chlorite, with variable amounts of quartz, feldspar, and organic matter. The texture is dominated by microscopic layering, and the rock splits into laminae when broken, a property called fissility. Colors reflect mineral content and the presence of organic matter or iron compounds.

Formation and metamorphism: shale forms by diagenetic compaction of mud in quiet-water environments, such as deep lakes, lagoons, or offshore settings. Under low-grade regional metamorphism, shale is transformed into slate, a harder rock used for roofing and building. Shale enriched in organic matter can become oil shale, from which hydrocarbons are produced by heating or pyrolysis.

Uses and distribution: shale is a common building material, especially for bricks and decorative stones; slate is widely used for roofing. Oil shale deposits are exploited in some regions to extract shale oil, though the process has environmental considerations. Globally, skifer occurs in many sedimentary basins and serves as an important unit in stratigraphy and petroleum geology.