Igneous Rocks by Composition

Igneous rocks are classified according to their mineral content:

Within these four groups, rocks are named depending on whether they display coarse-grained or fine-grained textures. The coarse-grained textures indicate intrusive rocks whereas the fine-grained textures generally indicate extrusive rocks. Extrusive rocks defined mainly by texture are discussed under rock textures: obsidian, scoria, pumice, tuff, and volcanic breccia.

Coarse-Grained Textures

Fine-Grained Textures

Peridotite

=

Ultramafic

Komatiite

(Ultramafic, but too rare to worry about at this point in your life)

Gabbro

=

Mafic

Basalt

=

Mafic

Diorite

=

Intermediate

Andesite

=

Intermediate

Granite

=

Felsic

Rhyolite

=

Felsic

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