Zeolite

Zeolite (Gr. zēō, 'I boil'), the common name of a large group of minerals, often called the Zeolitic family. They receive this name from their melting and bubbling up before the blowpipe. They are all soluble in acids, and most of them gelatinise in acids in consequence of silica being set free. They are hydrated silicates of alkalies or alkaline earths, most of them containing alumina. Magnesia is rarely present in them. Their composition, however, is very various. They are generally found in amygdaloidal cavities, or in fissures of basalt, porphyrite, &c., and occasionally also in granite, gneiss, and other crystalline schists and altered rocks, apparently as deposits from water percolating through the rock. They sometimes, but rarely, occur in veins. They are found either in crystals or of crystalline structure, often in plates or fine scales, often in needles or fibrous. Among them are Analcime, Natrolite or Mesotype, Scolezite, Thomsonite, Stillbite, Heulandite, Phillipsite, Gmelinite, Chabasite, Harmotome or Cross-stone, Apophyllite and Laumonite. The number of species and varieties which have been described and have received distinct names is very large.