L351 Limestone, mudstone, micrite, chalk

This white rock is virtually pure carbonate. It fizzes with acid. It is fine-grained and poorly cemented, making it soft and low density. It is commonly known as ‘chalk’.

Very uniform cryptocrystalline carbonate. 
Rare larger calcite crystals <0.5mm.

Very fine-grained, so deposited in a very low energy environment. 
Such fine carbonate could have been produced in one of two ways:
1. Tests of calcitic plankton. 
2. Very finely ground shell fragments. Currents alone could not grind the shells this finely. This would require bioerosion – e.g. fish ingesting organisms with carbonate shells, and grinding the carbonate to a fine powder.

limestone
mustone
micrite
chalk