Igneous Rock Identification


An igneous rock identification chart is shown below. Note that all rocks are identified by their texture and composition. For igneous rocks, texture is derived from the environment of cooling of the molten rock. Composition concerns the mineral components and roughly equates to whether light, intermediate, or dark colors.

texture light intermediate dark
PEGMATIC GRANITE PEGMATITE    
PHANERITIC GRANITE GRANODIORITE, DIORITE GABBRO
APHANITIC RHYOLITE ANDESITE BASALT
VESICULAR PUMICE
SCORIA
GLASSY OBSIDIAN
PYROCLASTIC
WELDED TUFF
PORPHYRYTIC the name is that of the ground mass with porphyry added