Instructor: Arthur Reed

Intrusive Igneous Rock Classification

(Last update: March 8, 2015)

Start Here	Color of rock	Mineralogy of rock	Rock Type
Fine grained (often porphyritic) â	Light-colored	Quartz, feldspars (white, light gray, or pink). Minor ferro-magnesian minerals.	Rhyolite (extrusive equivalent to granite)
	Medium-gray or medium-green	Feldspars (white or gray) and about 35-50% ferro-magnesian minerals. No quartz	Andesite (extrusive equivalent to diorite)
	Dark gray to black	Predominance of ferromagnesian minerals. Remainder of rock is plagioclase feldspar (medium to dark gray)	Basalt (extrusive equivalent to gabbro)
	Color of rock	Mineralogy of rock	Rock Type
Coarse grained â	Light-colored	Quartz, feldspars (white, light gray, or pink). Minor ferro-magnesian minerals.	Granite (intrusive equivalent to rhyolite)
	Medium-gray or medium-green	Feldspars (white or gray) and about 35-50% ferro-magnesian minerals. No quartz	Diorite (intrusive equivalent to andesite)
	Dark gray to black	Predominance of ferromagnesian minerals. Remainder of rock is plagioclase feldspar (medium to dark gray)	Gabbro (intrusive equivalent to basalt)

Based on information from the site of Pamela Gore, Department of Geology, Georgia Perimeter College