Chalk is used, all over the world, by teachers and children to write with on blackboards. Chalk is a soft and porous sedimentary rock that is a form of limestone. It is composed of calcium carbonate, also known as a mineral, calcite. Originally, chalk was an ‘animal’. Many kinds of tiny plants and animals cover the ocean waters. Out of these numerous organisms, one is called ‘Foraminifera’, a one-celled animal whose shell is made of lime. Their tiny shells go down to the ocean floor and settle there when the animal dies. These shells gradually form a thick layer, which slowly (over a million years) gets cemented. It is further compressed into a soft kind of limestone, called chalk. Chalk is also used in ceramics, cosmetics, crayons, plastics, rubber, paper, paints, etc.
