(1992).Īlkali feldspars comprise K-feldspar (K) and Na-feldspar or albite (Na). Sketch showing the 3D crystal structure of the unit cell of orthoclase feldspar. Other elements that may be present in small amounts include Fe 2+, Fe 3+, Ba, Ti, Mg, Sr, and Mn. Tetrahedral rings are distorted and deviate from the horizontal, allowing the formation of large sites in the feldspar structures that can accommodate large-radius ions of alkali elements (K +, Na +, and some Ca 2+). When stacked one on top of each other, the ‘rings’ produce an infinite framework of tetrahedrons, which can be imaged as infinite tetrahedron chains formed along two perpendicular directions. The structure of alkali feldspar can be visualized as a series of ‘rings’ of four tetrahedrons: in these rings, two neighboring tetrahedrons point up and the other two point down. Alkali feldspars are fundamental rock-forming K- and Na-bearing aluminosilicates that occur in many igneous, metamorphic, and sedimentary rocks, and constitute a significant portion of the ‘granitic’ continental crust.Īlkali feldspars are framework silicates characterized by a network of (Si,Al)O 4 tetrahedrons linked to one another in all directions.
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