Phonolite is an uncommon shallow intrusive or extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grained) to porphyritic (mixed fine- and coarse-grained). Phonolite is a variation of the igneous rock trachyte that contains nepheline or leucite rather than quartz. It has an unusually high (12% or more) Na2O + K2O content, defining its position in the TAS classification of igneous rocks. Its coarse grained (phaneritic) intrusive equivalent is nepheline syenite. Phonolite is typically fine grained and compact.
The name phonolite comes from the Ancient Greek meaning "sounding stone" due to the metallic sound it produces if an unfractured plate is hit; hence, the English name clinkstone is given as a synonym.
A few geological processes and tectonic events can melt the necessary precursor rocks to form phonolite. These include intracontinental hotspot volcanism, such as may form above mantle plumes covered by thick continental crust. A-type granites and alkaline igneous provinces usually occur alongside phonolites. Low-degree partial melting of underplates of granitic material in collisional orogenic belts may also produce phonolites.
Phonolite is common across Europe, particularly within the Eifel Plateau and the Laacher See. It is also found in the Czech Republic and the Mediterranean area near Italy. For localities in the United States, phonolite can be found in the Black Hills Forest in South Dakokta. The most well known phonolite-composed natural structure is the Devil's Tower, found in Wyoming.
Phonolites can be separated into slabs of appropriate dimensions to be used as roofing tiles in place of roofing slate. One such occurrence is in the French Massif Central region such as the Haute Loire département.
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