Image credit: Scott Brande
Video Introduction to Igneous Rock Classification
Watch this short video for an introduction to a simplified classification of the common igneous rocks.
Simplified Classification of Common Igneous Rocks
Nature's production over time of molten material in the planet is prodigious and widespread, from the eruption of molten liquid during volcanic activity, to the upward movement and intrusion of molten rock at the plate tectonic spreading centers.
A consequence of the heterogeneous composition of the planet is a bewildering diversity of chemical compounds in igneous rock. An equally bewildering diversity of physical and chemical environments occur throughout planet earth today, and during its geological history, resulting in different igneous rocks.
These two features are used in a simplified classification of the common igneous rocks.
texture - refers to properties of minerals or glass in the solid rock, such as the size, shape and layering of crystals
composition - refers to the chemistry of the minerals and materials in the solid rock
Geologists who specialize in the study of igneous rocks use these two factors, and others, to create highly specialized classifications in which rock names are arbitrarily assigned to narrow ranges of chemistry composition and texture.
As noted on the Home Page, this online study guide is being developed for students in a first introduction to physical geology. A necessity for a first introduction to the classification of the common igneous rocks is simplification, a loss of some accuracy, and the omission of significant details. A textbook or other references may be used as supplements to provide the additional knowledge lacking here.
The simplified classification table presented below focuses on features that may be observable without additional equipment (e.g., no hand-lenses, thin-sections, polarizing microscopes). As noted before, an advantage of digital online media is that images and video may be processed (e.g., zoomed) to partially substitute for the lack of hand lenses and low power microscopes.