Distinctive features:  
Unconsolidated or poorly consolidated white to black cindery ash of varying grain size.

Colour: 
Ranging from pure white to black.

Texture and granularity: 
Pyroclastic. Unconsolidated when fresh, but consolidating to form hard volcanic tuff.

Composition: 
Dependent on the composition of the source of magma. Mostly basaltic (black) to trachytic (white).

Field associations: 
As stratified beds of air-fall material ejected by volanic eruptions, sometimes unstratified when formed from ash flows.

Varieties:
Basaltic ash, which is coarse, cindery to fine black ash; trachytic (syenitic) ash, which is coarse, cindery to fine creamy white ash; and tuff, which is dense, varying from cream to yellow.

 

Worldwide and always associated with volcanoes.

 

Prefabricated building blocks, road surfacing, abrasives.