The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content.
A notable exception where feldspathoids and quartz-bearing rocks are found together is the Red Hill Syenite.
[1] Foid, a contraction of the term feldspathoid, is applied to any igneous rock containing up to 60% modal feldspathoid minerals.
Such terminology is used in the Streckeisen (QAPF) classification of igneous rocks.
This article about a specific silicate mineral is a stub.