Different types of limestone include marble, chalk, and __________.

Calcium carbonate (CaCO₃) is a common mineral that occurs naturally in many forms, including limestone, chalk, and marble. These different forms of calcium carbonate are formed through different geological processes and have different properties and uses:

1. Limestone: Limestone is a sedimentary rock that is primarily composed of calcium carbonate.
2. Chalk: Chalk is a soft, white, porous form of calcium carbonate that is formed from the accumulation of microscopic marine organisms such as plankton. 
3. Marble: Marble is a metamorphic rock that is formed from the recrystallization of limestone under high pressure and temperature.