Igneous Rock Classification

Texture vs. composition

	Felsic	Intermediate	Mafic	Ultramafic
Aphanitic fine grain	Rhyolite	Andesite	Basalt	Conditions needed to produce ultramafic flows do not exist in nature at this time.
Intermediate		Dacite	Diabase
Phaneritic coarse grain	Granite	Diorite	Gabbro	Peridotite
Glassy	Obsidian
Frothy	Pumice		Scoria

 

It is important to note that there are many, many intermediate steps between these main divisions. Geology is a science full of "shades of gray," and the naming of igneous rocks is certainly no exception.

You are visitor number since April 1, 1997