krétával

Krétával, also known as chalk, is a soft, white, or lightly colored sedimentary rock composed mostly of the mineral calcite. It is formed from the accumulation of skeletal fragments of marine organisms, primarily coccolithophores, a type of algae, over millions of years. The name derives from the Greek word *kréas*, meaning "fat," due to its smooth, greasy feel when rubbed.

Chalk is widely used in various applications, both historically and in modern times. One of its most common uses is as a writing tool, particularly in schools, where it is applied to blackboards or chalkboards. Its fine, powdery texture makes it ideal for creating smooth, erasable lines. Chalk is also used in art, such as pastel drawing, where its softness allows for delicate shading and blending.

In agriculture, chalk is sometimes applied to soil to improve drainage and reduce compaction. It can also be used as a natural pesticide, as the fine particles can deter certain pests. Additionally, chalk has been utilized in construction, where it is sometimes mixed with mortar to enhance workability or as a decorative element in plaster.

Geologically, chalk is a significant rock type found in many parts of the world, particularly in regions with ancient seabeds. Notable chalk formations include the White Cliffs of Dover in England and the cretaceous deposits in parts of France and Germany. These formations are often rich in fossils, providing valuable insights into prehistoric marine life.

While generally non-toxic, chalk should be used with caution, as inhaling large amounts of dust can irritate the respiratory system. Proper ventilation and protective measures are recommended when handling it in large quantities.