Craie

Craie is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. It is typically composed of coccoliths, which are the microscopic skeletons of coccolithophores, a type of plankton that lived in the oceans during the Cretaceous period. Craie is known for its friability and its tendency to crumble easily.

The formation of craie deposits is primarily associated with chalk seas that covered large parts of Europe during the Late Cretaceous epoch. Over millions of years, the accumulation of coccoliths on the seabed, along with other marine sediments, compacted and lithified to form thick layers of chalk. Significant deposits are found in countries like England, France, and Denmark.

Historically, craie has been used for a variety of purposes. Its most common use was as a writing implement, hence the English word "chalk." School chalk is often made from gypsum, but historically, craie itself was pulverized and molded into sticks for writing on blackboards. It has also been used as a building material, particularly in the construction of white cliffs, such as the White Cliffs of Dover. Furthermore, craie has applications in agriculture as a soil conditioner to neutralize acidity and in industry as a filler in plastics, paints, and paper.