perlite

perlitic /perr lit"ik/, adj.
/perr"luyt/, n. Petrog.
a volcanic glass in which concentric fractures impart a distinctive structure resembling masses of small spheroids, used as a plant growth medium.
Also, pearlite.
[1825-35; < F; see PEARL1, -ITE1]

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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 с 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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▪ natural glass
also called  Pearlstone,  

      a natural glass with concentric cracks such that the rock breaks into small, pearllike bodies. It is formed by the rapid cooling of viscous lava or magma. Perlite has a waxy to pearly lustre and is commonly gray or greenish but may be brown, blue, or red.

      Some perlites are of intrusive origin (dikes), but others constitute major portions of lava flows. These glassy rocks may grade into nearly completely crystalline volcanic types. Like obsidian, they may contain large crystals (phenocrysts) of quartz, alkali feldspar, plagioclase feldspar, and, in some cases, biotite or hornblende; where phenocrysts are abundant the rock passes into vitrophyre.

      Perlite is a type of rhyolite with a chemical composition, index of refraction, and specific gravity similar to those of obsidian. Its water content, however, is considerably higher (generally 3 to 4 percent); much of it is absorbed, subsequent to consolidation, from the sea or from wet sediments into which the perlite was intruded.

       devitrification, or conversion of the glass to a microscopically fine crystalline aggregate, is usually initiated spontaneously along cracks or at the surfaces of phenocrysts and crystalline bodies (spherulites). Some minutely crystalline rocks show well-developed perlitic structure and undoubtedly represent completely devitrified perlite. The localization of spherulites along curved and concentric bands in certain glass-free rocks suggests a devitrified perlite with spherulitic growth along the perlitic cracks.

      Before about 1950 perlite was virtually unknown in commerce. Since then, however, great deposits have been worked in New Mexico, Nevada, California, and other western states; production outside the United States has increased very slowly, the chief producers being Greece and Turkey. When crushed perlite is rapidly heated, the contained water is converted to steam; tiny bubbles are formed within the softened rock, and the perlite is thus expanded up to 20 times its original volume. Because of its very low density, heat-treated perlite is a substitute for sand in lightweight wall plaster and concrete aggregate. The porous nature of perlite makes the material ideal for heat and sound insulation; other uses include lightweight ceramic products, filters, and fillers.

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Universalium. 2010.

Look at other dictionaries:

  • Perlite — is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently.Properties and usesWhen it… …   Wikipedia

  • perlite — [ pɛrlit ] n. f. • 1812; de perle 1 ♦ Minér. Silicate naturel, pauvre en eau, de la famille des feldspaths. 2 ♦ (v. 1960) Techn. Constituant microscopique des alliages ferreux. Fonte à perlite. ● perlite nom féminin (de perle) Rhyolite vitreuse… …   Encyclopédie Universelle

  • Perlite — Per lite, n. (Min.) Same as {Pearlite}. [1913 Webster] …   The Collaborative International Dictionary of English

  • perlite — [pʉr′līt΄] n. [Fr < perle,PEARL1] 1. Geol. a greenish volcanic glass, similar to obsidian, with a pearly luster and multiple, minute concentric cracks, used as insulation and in making concrete, plaster, etc. 2. PEARLITE perlitic [pər lit′ik]… …   English World dictionary

  • Perlite — Perlit (vulkanisches Glas) mit weißem, pudrigen Aussehen Perlit (englisch: perlite) bezeichnet in den Geowissenschaften ein alteriertes (chemisch und physikalisch umgewandeltes) vulkanisches Glas (Obsidian) und zählt damit zu den Gesteinen. Die… …   Deutsch Wikipedia

  • Perlite — Cette page d’homonymie répertorie les différents sujets et articles partageant un même nom. La perlite est un constituant biphasé de l acier. La perlite est une roche naturelle à base de silice. Catégorie : Homonymie …   Wikipédia en Français

  • perlite — per·lì·te s.f. 1. TS petr. roccia effusiva acida costituita principalmente da vetro disposto in concrezioni simili a perle che si formano durante il raffreddamento, utilizzata come isolante termoacustico 2. TS metall. eutettico di ferrite e… …   Dizionario italiano

  • perlite — GLOSSARY OF VOLCANIC TERMS Hydrated obsidian, generally light grey in color, that is commonly characterized by rounded, onion skin like fractures (perlitic cracks). Apache s tears are unhydrated clumps of fresh obsidian that are commonly found… …   Glossary of volcanic terms

  • perlite —   n. volcanic glass forming, when expanded by heat, an insulating material and a light weight aggregate added to concrete and plaster or used as soil conditioner.    ♦ perlitic, a. having perlite like texture …   Dictionary of difficult words

  • perlite — perlitas statusas T sritis chemija apibrėžtis Kaitinant išpūsti, 5–20 kartų padidėję rūgščiosios vulkaninės uolienos grūdeliai atitikmenys: angl. pearlite; perlite rus. перлит …   Chemijos terminų aiškinamasis žodynas

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