Tonalite
From Wikipedia, the free encyclopedia
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 and quartz diorite with from 5 to 20% quartz.
Trondhjemite is an orthoclase deficient variety of tonalite with minor biotite as the only mafic mineral, named after Norway's third largest city, Trondheim.
 |
This article about a specific mineral, mineraloid, or rock type is a stub. You can help Wikipedia by expanding it. |
