Distinctive features:  
Whitish compact rock that effervesces in dilute hydrochloric acid. Often rich in fossils.

Colour: 
White to yellowish or grey. Black varieties are rich in hydrocarbons.

Texture and granularity: 
Variable; compact, oolitic, crystalline, earthy-granular, pisolitic, shelly.

Composition: 
Mostly calcium carbonate.

Field associations: 
Deposited in ancient seas by precipitation or by the accumulation of calcite-rich shells etc., coral reefs, around hot springs.

Varieties:
Crystalline limestone, which has granoblastic calcium carbonate crystals; crinoidal limestone, which is rich in fragments of fossil crinoids; oolitic limestones, which has tiny ooliths of calcium carbonatel pisolite, which has large (up to 4 mm / 1/8 in) ooliths; and reef limstone, which is rich in coral reef fossils.

 

Worldwide.

 

Source of cement, building construction (locally), blackboard chalk.