Perlite

perlite

 or pearlstone

Natural glass with concentric cracks such that the rock breaks into small, pearl-like bodies. It is formed by the rapid cooling of viscous lava or magma. Perlite is porous and has a waxy to pearly lustre and is commonly gray or greenish but may be brown, blue, or red. Since c. 1950, large deposits have been worked in New Mexico, Nevada, California, and other western states. Heat-treated perlite is a substitute for sand in lightweight wall plaster and concrete aggregate. Perlite is used for heat and sound insulation, lightweight ceramic products, and filters.

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perlite [′pər‚līt]

(geology)

A rhyolitic glass with abundant spherical or convolute cracks that cause it to break into small pearllike masses or pebbles, usually less than a centimeter across; it is commonly gray or green with a pearly luster and has the composition of rhyolite. Also known as pearlite; pearlstone.

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perlite

A siliceous volcanic rock; under heat it expands to 15 to 20 times its original volume, forming an excellent lightweight aggregate; used in plaster or gypsum wallboard, as loose-fill thermal insulation, and as an aggregate in concrete.

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Perlite 

an acid volcanic glass with fine, concentric cracks along which a specimen breaks into small pebbles that sometimes have a pearly luster; such cracks are characteristic of perlitic structure.

The composition of perlite resembles that of acid lavas, for example, liparite and dacite, which are chiefly composed of 65 to 75 percent SiO₂ and 10 to 15 percent Al₂O₃ and which also include admixtures of Fe₂O₃, CaO, MgO, SO₃, and R₂O in proportions that range from fractions of a percent to single percentage units. Perlite can also contain as much as 3 to 6 percent constitutional water, that is, water which is bound into hydrated crystals. When crushed perlite is rapidly heated, the enclosed water evaporates, thus swelling the softened rock and increasing the specimen’s volume ten to 20 times. The swelling temperature of perlite, which depends on the water content and chemical composition, ranges from 850°C to 1000°C and sometimes reaches 1200°C. Expanded perlite grains have a low density that ranges from 70 to 600 kg/m³; they are thus suitable for use as sand or rubble in aggregates for lightweight concrete as well as in heat-insulating products, for example, those made from perlite and bitumens, perlite and silicates, and perlite and ceramics. Expanded perlite is also used in the chemical, petroleum-refining, food, and pharmaceutical industries and in glassmaking and agriculture.

Perlite is widely used in many countries throughout the world. The USSR has aggregate geological reserves of perlite that are estimated at approximately 500 million m³. More than 600,000 m³ of perlite was extracted in 1974, including 427,000 m³ from the Aragats deposit in the Armenian SSR, 110,000 m³ from the Beregovo deposit in the Ukrainian SSR, and 66,000 m³ from the Mukhor-Tala deposit in the Buriat ASSR.

V. M. BORZUNOV