A story of the Cretaceous period
Chalk is a poorly compacted sedimentary rock, whose diagenesis is incomplete. The sediments from which chalk originates are predominately composed of compacted coccoliths (a lime-secreting algae).
Minor compaction by later sediments becoming harder with formation of flints. (Source: Imerys Performance Minerals)
Chalk is a soft, white, porous form of limestone composed of the mineral calcite and maybe yellowish, grey or white in colour. Chalk is obtained from numerous sites along the European chalk belt - from the UK through France all the way to the island of Rügen in north Germany.
The major chalk producing regions in the UK are centred on the high quality chalk deposits found in Humberside, Cambridgeshire/Suffolk and Wiltshire. These deposits were laid down during the Cretaceous period between 70 and 120 million years ago.