feldspathoid

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feldspathoid The name for a group of framework silicate minerals which are similar to feldspars in their structure but contain less silica per formula unit. The group includes the minerals nepheline (a sodic feldspathoid), leucite (a potassic feldspathoid), and sodalite (a sodium, chlorine-bearing feldspathoid). The mineral analcime, although a zeolite, is closely related to the feldspathoids and often described with them. Minerals within the feldspathoid group crystallize from silica-deficient (silica undersaturated) melts and can occur instead of, or with, feldspar.