Leucite(redirected from leucitic)
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a mineral whose chemical composition is K(AlSi2-O6); contains 21.58 percent K2O, 23.40 percent AI2O3, and 55.02 percent SiO2; often has admixtures of Na and Ca. Leucite is an aluminosilicate with a skeletal crystal lattice structure. It crystallizes in the isometric system and usually occurs in round crystals of isometric form. At temperatures below 605°C leucite changes to a tetragonal modification and forms finely twinned paramorphs along the crystals of the isometric leucite. Leucite is white in color with a grayish or yellowish tint. It has a hardness of 5–6 on Moh’s scale; its density is 2,450–2,500 kg/m3. It forms porphyritic phenocrysts in lavas rich in alkalis and low in silica. Leucite is found in lavas (for example, Mount Vesuvius). In the USSR it is found in certain effusive rocks in the Armenian SSR, central Kazakhstan, and Eastern Siberia.