A glassy mineral of the alkali feldspar group, typically occurring as tabular crystals.
- At temperatures above about 660°C complete solid solution occurs between the two alkali feldspar end-members sanidine and high albite, but below this there is a break and two feldspars of different composition occur together.
- The majority of the rhyolites are porphyritic and contain phenocrysts of one or more of the following: plagioclase, clinopyroxene, magnetite, quartz and sanidine, plus accessory apatite and zircon.
- Closer to the contact microcline is replaced by sanidine, and perthitic exsolution in detrital alkali feldspar begins to disappear.
Early 19th century: from Greek sanis, sanid- 'board' + -ine4.
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