Perlite mine, Voudia

Perlite is a volcanic glassy material formed when rapidly cooling high silicate (70-75%) lava entraps water in its mass. When heated to 800-950 'C, the material softens and the pressure from the entrapped water vapour bubbles leads to an about 7-16 fold increase in volume. This results in a very light-weight foam-like material.

 

www.photovolcanica.com/VolcanoInfo/Milos/Milos.html

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