Distinctive features:  
Spilts easily into thin plates along well-defined planes parallel to the original startification. Buff to grey very fine-grained silty rock.

Colour: 
Buff to various shades of grey.

Texture and granularity: 
Fine-grained.

Composition: 
Complex mixture of microscopic clay mierals, plus mica and quartz.

Field associations: 
Derived from ancient mud deposits, it occurs in most sedimentary sequences with fine sandstone and limestone.

Varieties:
Probably mudstone.

 

Worldwide.

 

Source of fossils.