Chalk is a soft, white, porous sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells (coccoliths) shed from micro-organisms called coccolithophores. Flint (a type of chert unique to chalk) is very common as bands parallel to the bedding or as nodules embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint).
Chalk is a form of calcium carbonate, having the same chemical composition as ground calcium carbonate, limestone, marble, and precipitated calcium carbonate (PCC).
Blackboard chalk used to be made of chalk, although now it's made from gypsum. In fact, the derivation of 'gypsum' is a Greek word for chalk, so the two minerals have got muddled in the past.
1.Finely prepared chalk, used as a drawing implement, most commonly in teaching. It can also be used in the Fine Arts; a drawing made with crayons. Red chalk, an indurated clayey ocher containing iron is also used by painters.
2. When heated, the calcium carbonate in limestone decomposes to lime, or calcium oxide. This is both used in the making of cement, it is a fertilizer for farmland and as a flux in smelting copper and lead ores and in making iron and steel.
3. Chalk line, a cord rubbed with chalk, used for making straight lines on boards or other material, as a guide in cutting or in arranging work.
4. Chalk mixture, a preparation of chalk, cinnamon, and sugar in gum water, has been much used in diarrheal affection, esp. of infants.
5. Gymnasts use chalk on all six aperatuses. It creates friction between the surfaces of the hands (or the feet, in the cases of floor and vault) and the aperatus, allowing gymnasts to perform their skills.
6. Chalk is used on snooker and pool cues.
7. Disused Chalk pits might be considerde for waste disposal, however, the high permeability of the Chalk means that this could only occur when the aquifer from which much drinking water is obtained is unaffected-therefore never.
