- Sanidine
Sanidine is the high temperature form of potassium
feldspar (K,Na)(Si,Al)4O8. [Mineral Handbook http://www.minsocam.org/msa/Handbook/Sanidine.PDF ] Sanidine most typically occurs infelsic volcanic rock s such asobsidian ,rhyolite andtrachyte . Sanidine crystallizes in themonoclinic crystal system.Orthoclase is amonoclinic polymorph stable at lower temperatures. At yet lower temperatures,microcline , atriclinic polymorph of potassium feldspar, is stable.Due to the high temperature and rapid quenching, sanidine can contain more sodium in its structure than the two polymorphs that equilibrated at lower temperatures. Sanidine and high
albite constitute asolid solution series with intermediate compositions termedanorthoclase . Exsolution of an albite phase does occur; resulting cryptoperthite can best be observed inelectron microprobe images.References
* Hurlbut, Cornelius S.; Klein, Cornelis, 1985, "Manual of Mineralogy", 20th ed., Wiley, ISBN 0-471-80580-7
* [http://www.webmineral.com/data/Sanidine.shtml Webmineral data]
* [http://www.mindat.org/min-3521.html Mindat]
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