close up micro-graphic of expanded perlite
perlite ore expanded light and frothy
perlite expansion furnace
hess perlite mine in southeast idaho

Perlite ore is a glassy volcanic rock with a vitreous, pearly luster and a characteristic concentric or perlitic fracture. Closely related to pumice, it differs from other volcanic glasses principally in its combined water content, which produces the unusual characteristic of expanding, or "popping," up to 20 times its original volume upon being exposed to rapid, controlled heating. Rapidly heating perlite ore to temperatures of about 900°C (1,700°F) softens the volcanic glass, causing entrapped water molecules in the rock to turn to steam and expand the particles like popcorn. The resulting expanded particles—actually clusters of minute glass bubbles—are spherical in shape, usually fluffy or frothy, highly porous due to a foam-like cellular internal structure, and have a very low density.

The expansion process also creates one of perlite's most distinguishing characteristics: its white color. While the crude rock may range from transparent light gray to glossy black, the color of expanded perlite ranges from snowy white to grayish white.

Perlite is a form of natural volcanic glass, and is classified as chemically inert, with a pH of approximately 7. Expanded perlite can be manufactured to weigh as little as 2 pounds per cubic foot (32 kg/m3) making it adaptable for numerous applications.

Low Impact; Sustainable Resource

The global perlite industry actively mines a total of less than 8 square km (3 sq miles)—about 1% of the total perlite deposits available worldwide. Perlite mining has limited environmental impact. There is little overburden to manage, minimal waste, and no chemicals are needed to process the ore. Once mined, perlite does not create by-products during expanding and processing, as only the physical form is altered. (download Perlite Sustainability Fact Sheet)

A Versatile Mineral

Expanded perlite exhibits very low thermal conductivity, low sound transmission, high fire resistance, a large surface area and low moisture retention. It is chemically inert, sterile, non-toxic and non-fibrous, free of organic impurities, and has a neutral pH. Regarded as an essentially "environmentally safe" building material, perlite is incredibly versatile and is used in a wide range of products and processes in industry. Read about the uses and applications of perlite.

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