Chalk thin section microscope slide composed of the debris of calcareous planktonic algae i.e. minute calcite shells known as Coccoliths which detach from micro-organisms known as Coccolithophores. Chalk is a soft, white, porous sedimentary carbonate rock; a form of micritic limestone. It forms under relatively deep, low energy conditions where the gradual accumulation of these calcareous organisms is permitted. These thin sections exhibit abundant coccolithophores within an even finer micritic matrix. This material is Cretaceous in age and it came from Yorkshire. The glass is 46 x 27 mm in size, supplied in a protective card sleeve with a label, ideal for microscopy, petrology & educational use.