(named after La Foia, a peak in the Serra di Monchi-que, in southern Portugal), a leucocratic, completely crystalline intrusive rock; an aegirine or hornblende variety of nepheline syenite. Foyaites consist of about 60 percent potassium feldspars, usually microcline-perthite and orthoclases, about 25–30 percent nepheline, and about 10 percent colored minerals, such as aegi-rine-augite, alkaline hornblende, and, very rarely, iron biotite. Foyaites usually contain ore minerals, titanite, apatite, and zircon. They are widely distributed in various alkaline rock complexes. Foyaite is used as a construction material.