Make your own free website on Tripod.com

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

 

 

 

 

Return to Geology Page