feldspaatides

Feldspatoids are a group of tectosilicate minerals, forming a subdivision of the feldspar group. They are chemically similar to feldspars but have a lower silica content. This lower silica content results in their crystallization in silica-undersaturated magmas, unlike feldspars which crystallize in silica-oversaturated magmas. Feldspatoids are therefore found in alkaline and ultrabasic igneous rocks such as nepheline syenites, phonolites, and alkali basalts. Common examples of feldspatoids include nepheline, leucite, sodalite, and haüyne. They are generally softer and less resistant to chemical weathering than feldspars. Feldspatoids can be found in various colors, often white, gray, or pale yellow, and may exhibit vitreous or greasy luster. Their presence in a rock indicates a magma that was poor in silica. While not as abundant as feldspars, feldspatoids are significant in petrology for understanding magma evolution and the classification of igneous rocks. Some feldspatoids, like sodalite, are also used as gemstones or for ornamental purposes, though their relative softness limits their widespread application.