Chalk
Description
!"Nitzana Chalk curves" situated at Western [Negev, Israel, are chalk deposits formed in the Mesozoic era's Tethys Ocean](//upload.wikimedia.org/wikipedia/commons/thumb/1/17/Nitzanachalkcurves%282%29%2CWesternNegev%2CIsrael.jpg/250px-Nitzanachalkcurves%282%29%2CWesternNegev%2CIsrael.jpg)
Description
!Open chalk pit, Seale, Surrey, UK
Description
Chalk is a fine-textured, earthy type of limestone distinguished by its light colour, softness, and high porosity. It is composed mostly of tiny fragments of the calcite shells or skeletons of plankton, such as foraminifera or coccolithophores. These fragments mostly take the form of calcite plates ranging from 0.5 to 4 microns in size, though about 10% to 25% of a typical chalk is composed of fragments that are 10 to 100 microns in size. The larger fragments include intact plankton skeletons and skeletal fragments of larger organisms, such as molluscs, echinoderms, or bryozoans.
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