Tonalite

A piece of tonalite on red granite gneiss from Tjörn, Sweden

Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with 10% or less alkali feldspar. Quartz is present as more than 20% of the rock. Amphiboles and pyroxenes are common accessory minerals.

In older references tonalite is sometimes used as a synonym for quartz diorite. However the current IUGS classification defines tonalite as having greater than 20% quartz, while quartz diorite varies its quartz content from 5 to 20%.

The name is derived from the type locality of tonalites, adjacent to the Tonale Line, a major structural lineament and mountain pass, Tonale Pass, in the Italian and Austrian Alps.

Trondhjemite is an orthoclase-deficient variety of tonalite with minor biotite as the only mafic mineral, named after Norway's third largest city, Trondheim.

External links

Media related to Tonalite at Wikimedia Commons

Common igneous rocks classified by silicon dioxide content

Type	Ultramafic <45% SiO₂	Mafic 45–52% SiO₂	Intermediate 52–63% SiO₂	Intermediate–felsic 63–69% SiO₂	Felsic >69% SiO₂

Volcanic rocks: Subvolcanic rocks: Plutonic rocks:	Komatiite, Picrite basalt Kimberlite, Lamproite Peridotite	Basalt Diabase (Dolerite) Gabbro	Andesite Microdiorite Diorite	Dacite Microgranodiorite Granodiorite	Rhyolite Microgranite, Aplite Granite

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This article is issued from Wikipedia - version of the 11/10/2015. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.