Distinctive features:  
Greyish, very fine-grained, foliated rocks that split into thin sheets. Sometimes contain well-formed pyrite crystals. Found in metamorphic environments.

Colour: 
Usually shades of medium to dark grey, but sometimes a buff colour.

Texture and granularity: 
Slaty and very fine-grained.

Composition:
Mica, quartz and other minerals that can be determined only by X-rays.

Field associations: 
In areas of regionally metamorphosed shale or volcanic tuff.

 

Worldwide.

 

Roofing sheets.