They are of trachytic appearance, containing phenocysts of sanidine, leucite, augite and biotite. Their commonest minerals are olivine, anorthite, hornblende, augite, biotite and leucite. At Vesuvius it occurs as alterations from gypsum within leucite tephrite and as fumarole deposits. It commonly occurs in association with orthoclase, sanidine, labradorite, olivine, leucite, amphiboles and other pyroxenes. They are associated principally with basalts, nepheline and leucite basalts and monchiquites. Examples include aluminosilicate glass, e.g. feldspathic, synthetic porcelain, and leucite reinforced ceramics. The plutonic leucite-bearing rocks are leucite syenite and missourite. Melanite is found in some of the lavas, as in the leucite syenites. Leucite lavas from which feldspar is absent are divided into the leucitites and leucite basalts. It is associated with other minerals typical of silica-undersaturated environments, namely leucite, cancrinite and natrolite. This pseudo-cubic character of leucite is very similar to that of the mineral boracite. Associated minerals include nepheline, leucite, titanian andradite, melilite, augite, sanidine, biotite, phlogopite and apatite. Leucite is common in lavas but very rare in plutonic rocks.