Feldspathoid

feldspathoid

Any of a group of alkali aluminosilicate minerals similar to the feldspars in composition but having a lower silica-alkali ratio or containing chloride, sulfide, sulfate, or carbonate. Their physical and chemical properties lie between those of the feldspars and zeolites. The most abundant feldspathoids are nepheline and leucite. Other significant varieties include kalsilite, sodalite, nosean, and haüynite. Feldspathoids are found chiefly in igneous and metamorphic rocks; they are used as raw materials in the production of alum, glass, and ceramics.

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feldspathoid [′fel‚spa‚thȯid]

(geology)

Aluminosilicates of sodium, potassium, or calcium that are similar in composition to feldspars but contain less silica than the corresponding feldspar.

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Feldspathoid 

a group of alkali rock-forming minerals (aluminosilicates) that are not as rich in silica as the feldspars. The structure of the feldspathoids characteristically includes additional anions, such as Cl^–, CO₃^2–, SO₄^2–, S^2–, and sometimes H₂O. The feldspathoids replace the feldspars in alkalic rocks and some basic rocks. The major feldspathoid minerals include nepheline, leucite, sodalite, nosean, haiiyne, and cancrinite.