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alkali feldspar

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alkali feldspar

Any of several common silicate minerals that often occur as whitish to variously coloured, glassy crystals. The alkali feldspars may be regarded as mixtures of sodium aluminosilicate (NaAlSi3O8) and potassium aluminosilicate (KAlSi3O8). Both the sodium and potassium aluminosilicates have several distinct forms, each with a different structure. Alkali feldspars are used in the manufacture of glass and ceramics; transparent, highly coloured, or iridescent varieties are sometimes used as gemstones. They are primarily important, however, as constituents of rocks (see plagioclase).

alkali feldspar [′al·kə‚lī ′feld‚spar]
(mineralogy)
A feldspar composed of potassium feldspar and sodium feldspar, such as orthoclase, microcline, albite, and anorthoclase; all are considered alkali-rich.
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A typical rapakivi texture consists of plagioclase-mantled alkali feldspar megacrysts (ovoids) and two generations of quartz and feldspar.
Surface weathering of rapakivi granite outcrops--implications for ... by Harma, Paavo; Selonen, Olavi / Estonian Journal of Earth Sciences
Plagioclase dramatically removes Sr at intermediate stages and alkali feldspars sequester Ba and Rb as late-stage trachytes and phonolites form in alkaline magmas.
Igneous rock associations 4. Oceanic island volcanism I mineralogy ... by Mallory-Greenough, Leanne M. / Geoscience Canada
As a rule, the alkali feldspar measurements give somewhat higher ages than OSL from quartz, which can be explained by slower bleaching of the feldspar in the sunlight exposure.
Application of OSL and [sup.10]Be techniques to the establishment of ... by Raukas, Anto / Proceedings of the Estonian Academy of Sciences: Geology
 
 
 
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