What is chaulk?

Chalk is a soft, white, porous sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is an ionic salt called calcium%20carbonate or CaCO3. Chalk forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores.

It is common to find chert or flint nodules embedded in chalk. Chalk is resistant to weathering and can form cliffs, such as the White Cliffs of Dover.

Chalk is used in a variety of applications including:

• Writing (on blackboards, though this is often made of gypsum now)
• Agriculture (for raising pH in acidic soils)
• Construction (as a component of cement and mortar)
• Polishing