Feldspar

Feldspar is a group of rock-forming aluminosilicate minerals containing potassium, sodium, or calcium. Its members are major constituents of Earth's crust and occur in igneous, metamorphic, and sedimentary rocks.

Aluminosilicate: A mineral or material built from linked aluminum- and silicon-centered oxygen structures. Feldspars belong to this broad mineral-chemical family.
Solid solution: A crystal structure in which one chemical element can substitute for another across a compositional range. Feldspar series form as potassium, sodium, and calcium vary in compatible structures.
Bowen's reaction series: A model describing the sequence in which common silicate minerals crystallize from cooling magma. Feldspar types help mark magma crystallization conditions in this sequence.
Orthoclase: A potassium feldspar with monoclinic crystal symmetry. It is a common potassium-rich feldspar in granites and other rocks.
Tectosilicate: A silicate mineral whose silicon-oxygen tetrahedra form a three-dimensional framework. Feldspar’s framework structure places it among tectosilicates.
Alkali feldspar series: The potassium-sodium feldspar compositional range, with mixing limited at many temperatures. Its incomplete mixing helps produce distinct potassium- and sodium-rich feldspars.
Chemical weathering: The breakdown or alteration of minerals through chemical reactions at Earth's surface. Feldspar alteration is a major source of clay and dissolved ions.
Microcline: A potassium feldspar with triclinic crystal symmetry. Its crystal structure distinguishes it from orthoclase despite similar composition.
Plagioclase: A feldspar solid-solution series ranging from sodium-rich albite to calcium-rich anorthite. This series captures the sodium-to-calcium range within feldspars.
Perthite: An intergrowth of sodium-rich feldspar within potassium-rich feldspar, formed by unmixing during cooling. Cooling can separate an initially mixed alkali feldspar into this texture.

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