Tonalite

Photographed by Michael P. Klimetz

(Lightly Foliated)

Wisconsin Rapids

Wood County

WISCONSIN

Photographed by Michael P. Klimetz

(Lightly Foliated)

Wisconsin Rapids

Wood County

WISCONSIN

Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with a 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. Tonalite is sometimes synonymous with quartz diorite. However the current IUGS classification defines tonalite as having greater than 20% quartz and quartz diorite possesses from 5 to 20% quartz. 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.