|CroninProjects.org/ Vince/ PhysGeoLab/ igrox.index.html|
Basalt with columnar jointing along the Deschutes River in central Oregon. Photo by Vince Cronin.
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.
|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|
|alkali feldspar||biotite||plagioclase feldspar||quartz|
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