dioritic

Diorite is a coarse-grained intrusive igneous rock with an intermediate mineralogical composition. It is dominated by plagioclase feldspar and one or more dark minerals, typically hornblende (amphibole) and/or biotite, with little or no quartz.

The texture is phaneritic, meaning the crystals are large enough to be seen with the naked eye, reflecting slow cooling beneath the surface. Diorite’s color is usually medium gray to dark gray and often has a salt-and-pepper appearance from the contrast between light plagioclase crystals and dark ferromagnesian minerals.

Geologically, diorite forms from the crystallization of magma with intermediate composition. It is the intrusive analogue of andesite and commonly occurs in plutons, stocks, and dikes within continental crust, frequently in volcanic arc settings associated with subduction.

Quartz is typically low in diorite. When significant quartz is present, the rock is called quartz diorite, and rocks with more quartz and alkali feldspar may be classified as granodiorite. Diorite commonly occurs in conjunction with other plutonic rocks within batholiths and complex igneous intrusions.