Phonolite

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Phonolite, sometimes known as Clinkstone is an igneous, volcanic (extrusive) rock, of intermediate (between felsic and mafic) composition, with aphanitic to porphyritic texture. Mineral assemblage is usually abundant feldspathoids and alkali feldspar, and lesser plagioclase, as illustrated by the position of the field for phonolite in the QAPF diagram. Biotite, amphibole and pyroxene are common accessory minerals. Quartz is absent, because alkalis are enriched relative to silica, as illustrated by the position of phonolite in the TAS classification.

Phonolite is a fine-grained equivalent of nepheline syenite, and the genesis of such magmas is discussed in the treatment of that rock type.

Some phonolite outcrops make a musical sound when struck -- hence the name.

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