Kréta

Kréta, or chalk in English, is a soft, white to grayish-white porous sedimentary rock composed primarily of calcite (calcium carbonate). It forms from the accumulated microscopic shells of marine organisms, such as coccolithophores, which settle to the sea floor and lithify over millions of years. Chalk is fine-grained, low in density, and readily crumbles into a powder. It effervesces with dilute acids due to its calcite content.

Geology and occurrence: The most famous chalk deposits are in Europe, including large formations that create features like the White Cliffs of Dover and the surrounding downs in southern England. Chalk beds can occur with interbedded flint or marl within broader sedimentary sequences and are part of relatively extensive fossil-rich marine deposits.

Properties and varieties: Chalk is typically white or light-colored, with a soft Mohs hardness around 1–2. It contains carbonate minerals and often shows a porous, crumbly texture. Purity varies by source, which affects its suitability for different uses, from art to industrial applications.

Uses: Chalk has long been used for writing (chalk sticks for classrooms and art chalks). Industrially, it serves as a filler and whitening agent in paper, paint, and plastics; as a soil amendment to raise pH; and as a safe abrasive in certain toothpaste and cosmetic products when purity requirements are met. Chalk-derived lines and markers are also used in sports and construction.

Safety and handling: Chalk dust can irritate the respiratory system and eyes; dust control is recommended in occupational settings. Chalk is broadly non-toxic, but ingestion of large amounts may cause digestive discomfort. In all cases, purity and suitability depend on the intended use. In Hungarian, kréta denotes chalk as described here.