Distinctive features:  
Black, opaque volcanic glass that may contain irregular, whitish clusters of minerals. Resembles pitch in appearance.

Colour: 
Dull black.

Texture and granularity: 
Glassy and breaks to produce poorly defined conchoidal fracture.

Composition: 
Glass with the same chemical compositionas granite, syenite or granodiorite.

Field associations: 
Pitchstone originated form a rapidly chilled lava flow and is therefore always associated with volcanoes.

Varieties:
Obsidian, which is bright black glass with no phenocrusts; pumice, which is highly vesiculated glass; and vitrophyre, which is galss with tiny phenocrysts.

 

Worldwide, but particularly in Iceland, Italy, Lipari, Japan, Mexico, New Zaland, Russia, USA (Yellowstone Park, California, Oregon, Utah, New Mexico, Hawaii and lesser amounts in other states).

 

Aggregate.