PEGMATITIC TEXTURE
(EXTREMELY COARSE-GRAINED) | ||
|---|---|---|
| Overall Color | Most Common Minerals | Rock Name |
| light (felsic) | Na-plagioclase, orthoclase, quartz, biotite, amphibole, muscovite | pegmatite |
PHANERITIC TEXTURE
(COARSE-GRAINED) | ||
| Overall Color (composition) | Most Common Minerals | Rock Name |
| light (felsic) | Na-plagioclase, orthoclase, quartz, biotite, amphibole, muscovite | granite |
| medium-light (felsic) | Na-plagioclase, quartz, amphibole, biotite, orthoclase | granodiorite |
| medium-dark (intermediate) | Na-plagioclase, amphibole, pyroxene, biotite | diorite |
| dark (mafic) | Ca-plagioclase, pyroxene, olivine, amphibole | gabbro |
| APHANITIC TEXTURE (FINE-GRAINED) Originates in lava flows (or very shallow intrusions), which cool rapidly |
||
| Overall Color | Most Common Minerals | Rock Name |
| light (felsic) | Na-plagioclase, orthoclase, quartz, biotite, amphibole, muscovite | rhyolite |
| medium-light (felsic) | Na-plagioclase, quartz, amphibole, biotite, orthoclase | dacite |
| medium-dark (intermediate) | Na-plagioclase, amphibole, pyroxene, biotite | andesite |
| dark (mafic) | Ca-plagioclase, pyroxene, olivine, amphibole | basalt |
FROTHY TEXTURE
(POROUS, PUMICEOUS) |
||
| Overall Color | Most Common Minerals | Rock Name |
| light (felsic) | glass (may contain a few minerals common in felsic rocks, listed above) | pumice |
| dark (red or black) (mafic) | glass (may contain a few minerals common in mafic rocks, listed above) | scoria |
| Note: basalt with a smaller number of holes, known as vesicles, is called vesicular basalt. | ||
| GLASSY TEXTURE Originates from cooling too rapid to allow crystal lattices to form |
||
| Overall Color | Most common Minerals | Rock Name |
| black (white, red) (felsic) | glass (no minerals) | obsidian |
| FRAGMENTAL TEXTURE, COARSE-GRAINED
(CONTAINS LARGE ROCK FRAGMENTS) Originates from pyroclastic (explosive) eruptions |
||
| Overall Color | Most common Minerals | Rock Name |
| any (felsic, intermediate, or mafic) | variable (depending on rock fragments and ash content) | volcanic breccia |
| FRAGMENTAL TEXTURE, FINE-GRAINED
(MAINLY VOLCANIC ASH) Originates from pyroclastic (explosive) eruptions |
||
| Overall Color | Most common Minerals | Rock Name |
| light (felsic) | may contain a few minerals common in felsic rocks, listed above | rhyolitic tuff |
| medium (intermediate) | may contain a few minerals common in intermediate rocks, listed above | andesitic tuff |
| dark (mafic) | may contain a few minerals common in mafic rocks, listed above | basaltic tuff |
Igneous rock is solidified magma. Plutonic igneous rock comes from magma that intrudes within the earth, deep underground, and cools and crystallizes there. Volcanic igneous rock originates from magma that erupts, as either lava or as tephra, and turns solid on the earth's surface.
There are two categories of volcanic rock: (1) the effusive (lava flow) type of volcanic rock, which flows onto the earth's surface as lava and turns solid there, and (2) the pyroclastic (explosive) type of volcanic rock, which forms from volcanic material that explodes into the air and lands in pieces on the ground.
Igneous Rock Classification Table
© 2001 Ralph L. Dawes, Ph.D. and Cheryl D. Dawes
updated: 6/21/2020