- Also feld·spath·oi·dal. of or relating to a group of minerals similar in chemical composition to certain feldspars except for a lower silica content.
- a mineral of this group, as nepheline.
- any of a group of rock-forming minerals, such as leucite and sodalite, that are similar to feldspars but contain less silica
- Any of a group of relatively rare minerals that are chemically very similar to feldspars, but have too little silica to qualify as feldspars. Feldspathoids occur in igneous rocks with little or no silica.