Built from a 3D framework of corner-sharing AlO₄ and SiO₄ tetrahedra balanced by K⁺, Na⁺, or Ca²⁺ ions, feldspars compose about 60% of Earth's total crust and 41% of the continental crust by weight.
Compositions span three endmembers: potassium orthoclase/microcline (KAlSi₃O₈), sodium albite (NaAlSi₃O₈), and calcium anorthite (CaAl₂Si₂O₈), which form the alkali feldspar series and the continuous plagioclase series.
Chemical weathering of feldspar by carbonic acid hydrolysis produces clay minerals such as kaolinite, illite, and smectite, while unweathered feldspar serves as a primary flux in glassmaking and porcelain ceramics.