DESCRIPTION
In its natural state, Perlite occurs as a dense, gray to brown, glassy volcanic rock consisting essentially of fused sodium potassium aluminum silicate plus 3% to 5% water. When fractured and heated at high temperature (900° to 1100°) under proper conditions, it pops like popcorn, caused by the presence of occluded water, expanding to 20 or more times its original volume. The expanded material is crushed to yield a white, nonhygroscopic powder having a bulk density of 32 to 400 kg/m3 (2 to 25 lb/ft3) and a particle size ranging from less than one to several hundred micrometers. It is in this latter expanded and powdered state that Perlite is used as a filter aid in food processing. Acceptable food-grade free-flowing agents such as sodium carbonate and sodium silicate may be added. The powder is slightly soluble in water and sparingly soluble in dilute acids and alkalis.