CroninProjects.org/ Vince/ PhysGeoLab/ igrox.index.html

Basalt with columnar jointing along the Deschutes River in central Oregon.

Basalt with columnar jointing along the Deschutes River in central Oregon. Photo by Vince Cronin.

Igneous Rocks Home Page


Decision-tree graph for identifying igneous rocks: http://croninprojects.org/Vince/PhysGeoLab/IgRox-Table-V4.pdf

Click on the underlined links in the tables below to obtain more information about the igneous rock, texture or mineral, including some specimen pictures.

Igneous Rocks and Glasses

andesite gabbro obsidian rhyolite
basalt granite pumice tuff
diorite

Textures associated with igneous rocks

aphanitic: very fine grained
glassy: texture of broken glass
phaneritic: mineral grains are coarse/large enough to be distinct
porphyritic: larger grains in a finer-grained matrix or ground mass
pyroclastic: "fire broken" or blasted from a volcano
scoriaceous: low-density rock with very large number of small gas-bubble voids
vesicular: with gas-bubble voids frozen in rock at time of crystallization

Minerals commonly associated with igneous rocks

alkali feldspar biotite plagioclase feldspar quartz
amphibole olivine pyroxene

Return to the Dynamic Earth Lab home page.

If you have any questions or comments about this site or its contents, drop an email to the humble webmaster.
All of the original content of this website is © 2018 by Vincent S. Cronin