Earth Science

Earth Materials

Igneous Rock Classification
Study Tip
Composition starts with a C and Texture starts with a T. C comes before T in the alphabet, so composition must come before texture when classifying igneous rock.

Properties of Igneous Rock Compositions

Igneous rocks are classified by their composition (from felsic to ultramafic).

Study Tip
Composition starts with a C and Texture starts with a T. C comes before T in the alphabet, so composition must come before texture when classifying igneous rock.
Study Tip
The same way a person may cast a shadow over another person when they stand under the sun, planets or celestial bodies that have aligned themselves cast shadows over one another as well.

Properties of Igneous Rock Compositions

Composition
Color
Density
Minerals
Felsic
Light
Low
Quartz, orthoclase feldspar
Intermediate
Intermediate
Intermediate
Plagioclase feldspar, biotite, amphibole
Mafic
Dark
High
Olivine, pyroxene
Ultramafic
Very dark
Very high
Olivine

Texture

Igneous rocks are also classified by texture. Texture indicates how the magma that formed the rock cooled.

Silica Composition and Texture of Major Igneous Rocks

Silica Composition and Texture of Major Igneous Rocks

Type
Amount of Silica
Extrusive
Intrusive
Ultramafic
<45%
Komatiit
Peridotite
Mafic
45-52%
Basalt
Gabbro
Intermediate
52-63%
Andesite
Diorite
Intermediate-Felsic
63-69%
Dacite
Granodiorite
Felsic
>69% SiO₂
Rhyolite
Granite
Rhyolite
Rhyolite
Gabbro
Gabbro
Peridotite
Peridotite
Komatiite
Komatiite

Earth Science

Concept Check
  • How do scientists classify igneous rocks?
Supplemental Learning

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Properties of Igneous Rock Compositions

Composition
Color
Density
Minerals
Felsic
Intermediate
Mafic
Ultramafic