Tonalite
Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with alkali feldspar making up less than 10% of the total feldspar content. Quartz (SiO2) is present as more than 20% of the total quartz-alkali feldspar-plagioclase-feldspathoid (QAPF) content of the rock.<ref name="lebas-streckeisen-1991">Template:Cite journal</ref><ref name="bgs">Template:Cite journal</ref> Amphiboles and biotite are common in lesser quantities, while accessory minerals include apatite, magnetite and zircon.<ref>https://geologyscience.com/rocks/igneous-rocks/intrusive-igneous-rocks/tonalite/ Tonalite Page in Geology Science</ref><ref>Template:Cite book</ref>
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%.<ref name="lebas-streckeisen-1991"/>
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. The name was first applied by Gerhard vom Rath in 1864.<ref>Template:Cite book</ref> The term adamellite was originally applied by A. Cathrein in 1890 to orthoclase-bearing tonalite (likely a granodiorite) at Monte Adamello, Italy, in 1890, but later came to refer to quartz monzonite, and is now a deprecated term.<ref>Template:Cite journal</ref>
Trondhjemite is an orthoclase-deficient variety of sodium-rich tonalite with minor biotite as the only mafic mineral, named after Norway's third largest city, Trondheim.Template:Sfn
Tonalites, together with granodiorites, are characteristic of calc-alkaline batholiths formed above subduction zones.<ref>Template:Cite journal</ref>
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