Feldspatoids

Feldspathoids are a group of tectosilicate minerals within the feldspar group. They are chemically similar to feldspars but have a lower silica content. This lower silica content causes them to crystallize in the absence of quartz. Feldspathoids are typically found in silica-poor igneous rocks such as basalts, phonolites, and nephelinites. They are also found in some metamorphic rocks and in meteorites.

The most common feldspathoids include nepheline, leucite, sodalite, nosean, hauyne, and cancrinite. These minerals often occur together and can be difficult to distinguish in hand samples due to their similar appearance. They are typically white, gray, or colorless, and can be transparent to opaque.

Feldspathoids have some industrial uses. Nepheline is used in the glass and ceramic industries as a flux. Sodalite is sometimes used as a gemstone. The occurrence of feldspathoids in igneous rocks is significant for petrologists as it indicates the magma from which the rock crystallized was undersaturated in silica. This provides clues about the source region and melting processes of magmas. Their presence can also influence the weathering behavior of rocks.