Robert M. Hazen, in Progress in Biological Chirality, 2004. 3.2 Alkali Feldspar. Feldspars, including the alkali feldspar series (Na,K)AlSi 3 O 8 and the plagioclase feldspar series (NaSi,CaAl)AlSi 2 O 8, are among the most common rock-forming minerals in Earth’s crust [24, 25].These framework aluminosilicates are major constituents of most igneous rocks and they provide the principal ...