Albite is classified as a Feldspar Group Tectosilicate and is the sodic end member of both the plagioclase (Na-Ca) and the alkali (Na-K) feldspar series. The plagioclase series ranges in chemical composition from pure NaAlSi3O8 to pure CaAl2Si2O8 (Anorthite) while the alkali series ranges from albite to orthoclase KAlSi3O8.
Albite is comprised of an interconnected framework of three SiO4 and one AlO4 tetrahedra, with all oxygens shared between tetrahedra. The remaining negative charge is balanced by Na+, which fills larger voids in the structure. The silicon to oxygen ratio is 1:2. The exact structure of albite changes based on the ordering of the Al within the framework. High albite (formed at high temperatures) is triclinic and has a highly disordered Al/Si ordering. A monoclinic variety known as monalbite with a totally disordered Al/Si distribution also is known. Low albite, which forms at lower temperatures, is highly ordered and has a triclinic (C_1) structure. Na+ fills no less than 90%, and K plus Ca no more than 10%, of available voids. Albite exhibits twinning which can be seen as grooves on both the crystal and cleavage surfaces.
Highlighting FeaturesTetrahedral Si framework Tetrahedrally-coordinated Al atoms Tetrahedral framework Charge-balancing cations (Na) Single unit cell All atoms
Albite is a widely distributed white feldspar commonly found in granites, syenites, rhyolites, and trachytes, as well as pegmatites and spillites. Because albite is the last of the feldspars to crystallize from molten rock, it may often be found with other rare minerals. Major occurrences of albite can be found in Labrador, Canada, and the Scandinavian Peninsula. Albite is used for ornamental stone, as a component of ceramic clays, and for mineral specimens.
Importance in Soils
Feldspars are found in most soils and sediments and their composition can be used to infer the provenance of soil parent materials. The degree of feldspar weathering provides information about soil formation duration and process. The relatively easily weathered plagioclases are often the most important reserves of trace elements released to soils, particularly in sandy soils. The absolute quantity present in soils is an indicator of the degree of weathering. Strongly weathered soils have little or no feldspar, unless erosional/depositional processes add unweathered parent material.
Armbruster, T., H.B. Buergi, M. Kunz, E. Gnos, S. Broennimann, and C. Lienert. 1990. Variation of displacement parameters in structure refinements of low albite. American Mineralogist. 75:135-140.