Distinctive features:  
Whitish, porous rock that effervesces in dilute hydrochloric acid. Often contains bands of flint nodules and is rich in fossils.

Colour: 
White to yellowish or grey.

Texture and granularity: 
Fine-grained, earthy, crumbly, porous rock.

Composition: 
Mostly calcium carbonate, with minor amounts of fine silt.

Field associations: 
Deposited in ancient seas by the accumulation of tests (tiny shells) of microscopic marine organisms.

 

UK, France, Denmark.

 

As a source of cement.