What is phonolite in geology?
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What is phonolite in geology?
phonolite, any member of a group of extrusive igneous rocks (lavas) that are rich in nepheline and potash feldspar. The typical phonolite is a fine-grained, compact igneous rock that splits into thin, tough plates which make a ringing sound when struck by a hammer, hence the rock’s name.
What is phonolite made up of?
Phonolites: Phonolites are extrusive rocks that are essentially composed of alkali feldspar (Anorthoclase and Sanidine), mafic minerals such as alkali amphiboles, alkali pyroxenes, Augite, Biotite and Olivine) and one or more foids.
How phonolite rock is formed?
Formation. Unusually, phonolite forms from magma with a relatively low silica content, generated by low degrees of partial melting (less than 10%) of highly aluminous rocks of the lower crust such as tonalite, monzonite and metamorphic rocks.
What minerals are found in basalt?
Basalts are composed of minute grains of plagioclase feldspar (generally labradorite), pyroxene, olivine, biotite, hornblende, and less than 20% quartz. The mineral nepheline or leucite may associate or proxy the feldspar giving rise to verities with special names.
What minerals are in trachyte?
trachyte, light-coloured, very fine-grained extrusive igneous rock that is composed chiefly of alkali feldspar with minor amounts of dark-coloured minerals such as biotite, amphibole, or pyroxene.
How does phonolite porphyry form?
Phonolite is igneous—formed from magma. It’s often referred to as volcanic (e.g., here and here), which means it’s extrusive—magma reached the surface. And yet the Devils Tower and Rattlesnake Hills phonolite bodies are considered intrusions that formed below the surface, though probably not deep.
Is phonolite mafic or felsic?
Phonolite is a rare rock of intermediate chemical composition between felsic and mafic, with texture ranging from aphanites (fine-grain) to porphyritic (mixed fine- and coarse-grain).
Which mineral is more abundant in basalt?
Olivine and augite are the most common porphyritic minerals in basalts; porphyritic plagioclase feldspars are also found. Basaltic lavas are frequently spongy or pumiceous; the steam cavities become filled with secondary minerals such as calcite, chlorite, and zeolites.
Where is phonolite porphyry found?
The Cenozoic phonolite porphyry monolith forming Devils Tower is located in the western Black Hills in northeastern Wyoming (Fig.
What some identifying features of trachyte that make it an igneous rock?
Trachyte (/ˈtreɪkaɪt, ˈtrækaɪt/) is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and alkali metals. It is the volcanic equivalent of syenite.
How is trachyte formed?
What is the composition of trachyte?
Is trachyte a basalt?
Trachyte is the usual silica-rich end member of the alkaline magma series, in which alkaline basaltic magma experiences fractional crystallization while still underground.
