Definitions

1. noun

A type of igneous rock that is the most abundant type of intrusive rock, typically with a medium to coarse texture and a composition of 10 to 30% quartz, 55 to 70% plagioclase, and 5 to 20% orthopyroxene.

“The geologist studied the tonalite formation in the mountain range to understand its geological history.”

2. noun

A type of igneous rock that is intermediate in composition between gabbro and granite, often found in the roots of large granitic plutons.

“The tonalite formation in the region is a key indicator of the area’s tectonic history.”