Table 1: The Organization of Igneous Rocks
|
Subgroup ¢ |
Felsic |
Felsic |
Inter-mediate |
Inter-mediate |
Inter-mediate |
Mafic |
Ultrabasic |
|
Minerals ¢ |
(With quartz) |
(Little quartz) |
(No quartz) |
(No quartz) |
(No quartz) |
(No quartz) |
(No quartz) |
|
Origin ¤ |
More
orthoclase than plagioclase. Also
muscovite, biotite, amphibole, hornblende |
Orthoclase
in similar quantities as plagioclase.
Also biotite, amphibole, pyroxene, hornblende, augite |
More
plagioclase than orthoclase. Also
biotite, amphibole, pyroxene, augite, olivine, horn-blende, biotite |
No
feldspar. Few silicates. Pyroxene, olivine. |
|||
|
Course-grained: cooled slowly underground |
Pegmatite, Granite |
Syenite |
Monzonite |
Granodiorite |
Diorite |
Gabbro |
Peridotite, Dunite, Pyroxenite |
|
Porphyritic: cooled first below then above ground |
Granite Porphyry, Rhyolite Porphyry |
Syenite Porphyry |
Monzonite Porphyry |
Granodiorite Porphyry |
Andesite Porphyry |
Basalt Porphyry |
|
|
Fine-Grained: cooled quickly above ground |
Rhyolite |
Trachyte, Felsite |
Latite |
Dacite |
Andesite |
Basalt |
|
|
Glassy: cooled very quickly above ground |
Pumice |
|
Obsidian |
|
|
Scoria, Basalt Glass |
|
|
Fragmental: made of igneous fragments |
Tuff |
|
|
Volcanic Breccia |
|
|
|