Feldspathoid group

Nepheline (), also called nephelite, is a rock-forming mineral in the feldspathoid groupa silica-undersaturated aluminosilicate (Na3KAl4Si4O16) that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. It is used in glass and ceramic manufacturing and other industries, and has been investigated as an ore of aluminium.

Leucite (from the Greek word leukos meaning white) is a rock-forming mineral of the feldspathoid group, silica-undersaturated and composed of potassium and aluminium tectosilicate KAlSi2O6. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore pseudo-cubic. Goniometric measurements made by Gerhard vom Rath in 1873 led him to refer the crystals to the tetragonal system. Optical investigations have since proved the crystals to be still more complex in character, and to consist of several orthorhom

The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks, and are usually not found in rocks containing primary quartz. A notable exception where feldspathoids and quartz-bearing rocks are found together is the Red Hill Syenite.

Danalite is an iron beryllium silicate sulfide mineral with formula: Fe2+4Be3(SiO4)3S.

Kalsilite (KAlSiO4) is a vitreous white to grey feldspathoidal mineral that is found in some potassium-rich lavas, such as from Chamengo Crater in Uganda. It has a relative hardness of 5.5.