Instructor: Arthur Reed

 

Intrusive Igneous Rock Classification

(Last update: March 8, 2015)

 

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Color of rock

Mineralogy of rock

Rock Type

 

Fine grained

(often porphyritic)

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

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)

 

 

 


 

 

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