Foyaite

foyaite

[′fȯi·yə‚īt]
(petrology)
A nepheline syenite composed chiefly of potassium feldspar.

Foyaite

 

(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.

References in periodicals archive ?
In some areas, the foyaite is enriched by sodalite and villiaumite lenses up to 20 cm thick; these lenses lie between the pegmatite and the malignite layer.
Occurrence: In an aegirine-natrolite-microcline vein in foyaite.
Occurrence: In an intensely mineralized hyperagpaitic pegmatite intruded into foyaite.