Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. It forms under relatively deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores. It is common to find chert nodules embedded in chalk. Chalk can also refer to other compounds including magnesium silicate and calcium sulfate.
The Chalk Group (often just called the Chalk) is a lithostratigraphic unit (a certain number of rock strata) in the northwestern part of Europe. It is characterised by thick deposits of chalk, a soft porous white limestone, deposited in a marine environment during the Upper Cretaceous period. Chalk is a limestone that consists of coccolith biomicrite. A biomicrite is a limestone composed of fossil debris ("bio") and calcium carbonate mud ("micrite").
The Chalk Formation of Southern England is a system of chalk downland in the south of England. The formation is perhaps best known for Salisbury Plain, the location of Stonehenge, the Isle of Wight and the twin ridgeways of the North Downs and South Downs.
This is a list of the Sites of Special Scientific Interest (SSSIs) on the Isle of Wight, England. The Isle of Wight is an island and county three miles off the south coast of England in the English Channel. Its geology is complex, with a chalk downland ridge running east to west through its centre and important fossil beds from the Lower Cretaceous to the Lower Tertiary around the coast.