PEGMATITIC TEXTURE
(EXTREMELY COARSE-GRAINED) | ||
|---|---|---|
| Composition | Most Common Minerals | Rock Name |
| felsic | Na-plagioclase, orthoclase, quartz, biotite, amphibole, muscovite | pegmatite |
PHANERITIC TEXTURE
(COARSE-GRAINED) | ||
| Composition | Most Common Minerals | Rock Name |
| felsic | Na-plagioclase, orthoclase, quartz, biotite, amphibole, muscovite | granite |
| intermediate | Na-plagioclase, quartz, orthoclase, amphibole, biotite | granodiorite |
| Na-plagioclase, amphibole, pyroxene, biotite | diorite | |
| mafic | Ca-plagioclase, pyroxene, olivine, amphibole | gabbro |
| APHANITIC TEXTURE (FINE-GRAINED) Originates in lava flows (or very shallow intrusions), which cool rapidly |
||
| Composition | Most Common Minerals | Rock Name |
| felsic | Na-plagioclase, orthoclase, quartz, biotite, amphibole, muscovite | rhyolite |
| intermediate | Na-plagioclase, quartz, orthoclase, amphibole, biotite | dacite |
| Na-plagioclase, amphibole, pyroxene, biotite | andesite | |
| mafic | Ca-plagioclase, pyroxene, olivine, amphibole | basalt |
FROTHY TEXTURE
(POROUS, PUMICEOUS) |
||
| Composition | Most Common Minerals | Rock Name |
| felsic | glass (may contain a few minerals typical of felsic rocks) | pumice |
| mafic | glass (may contain a few mineral typical of mafic rocks) | scoria |
| Note: Basalt with fewer holes, known as vesicles, is called vesicular basalt. Scoria has more holes and may be black or red in color. | ||
| GLASSY TEXTURE Originates from cooling too rapid to allow crystal lattices to form |
||
| Composition | Most Common Minerals | Rock Name |
| felsic to mafic | glass (no minerals) | obsidian |
| Note: Obsidian that is transparent at thin edges and has good conchoidal fracture is probably felsic. | ||
| FRAGMENTAL TEXTURE--COARSE
(CONTAINS LARGE ROCK FRAGMENTS) Originates from pyroclastic (explosive) eruptions |
||
| Composition | Most Common Minerals | Rock Name |
| felsic to mafic | variable (depending on rock fragments and ash content) | volcanic breccia |
| FRAGMENTAL TEXTURE--FINE
(MAINLY VOLCANIC ASH) Originates from pyroclastic (explosive) eruptions |
||
| Composition | Most Common Minerals | Rock Name |
| felsic | may contain a few minerals typical of felsic rocks | rhyolitic tuff |
| medium | may contain a few minerals typical of intermediate rocks | andesitic tuff |
| mafic | may contain a few minerals typical of mafic rocks | basaltic tuff |
Geology 101 - Introduction to Physical Geology
Basics Table--Igneous Rock Classification
Created by Ralph L. Dawes, Ph.D. and Cheryl D. Dawes, including figures unless otherwise noted
updated: 5/28/13
Basics Table--Igneous Rock Classification
Created by Ralph L. Dawes, Ph.D. and Cheryl D. Dawes, including figures unless otherwise noted
updated: 5/28/13
Unless otherwise specified, this work by Washington State Colleges is licensed under a Creative Commons Attribution 3.0 United States License.