| Geology-208 |
| INTRUSIVE / PLUTONIC |
||||
| Rock |
Texture |
Origin |
Color |
Minerals |
|---|---|---|---|---|
| Granite (pink, white, graphic, porphyritic, hornblende) |
coarse-grained;
may be porphyritic cooled in two stages; slow-cooling over many Ka or Ma until solid |
beneath earth's surface; various depths |
light (felsic; >65% silica) |
quartz (20%),
K-feldspars (orthoclase & microcline), mica (muscovite or biotite),
Na-plagioclase |
| Granodiorite (granite family;also: pink, white) |
coarse-grained; may be porphyritic; cooled in two stages; slow-cooling over many Ka or Ma until solid |
beneath earth's surface; various depths |
light, medium (intermediate felsic) |
quartz, amphibole, mica (biotite), Na-plagioclase, hornblende |
| Diorite |
coarse-grained; may be porphyritic; cooled in two stages; slow-cooling over many Ka or Ma until solid |
beneath earth's surface; various depths |
medium, dark (intermediate mafic; 55-65% silica) |
Na & Ca-plagioclase, amphibole, hornblende, mica (biotite), pyroxene (augite) |
| Gabbro |
coarse-grained; may be porphyritic; cooled in two stages; slow-cooling over many Ka or Ma until solid |
beneath earth's surface; various depths |
medium (mafic; <10% silica) |
Ca-plagioclase, olivine, pyroxene (augite), magnetite |
| Volcanic Breccia |
coarse-grained; rock fragments (pyroclastic) |
transitional, water |
gray siliceous fragments in yellowish matrix (felsic) |
|
| EXTRUSIVE / VOLCANIC |
||||
| Rock |
Texture |
Origin |
Color |
Minerals |
| Andesite (amygdaloidal, porphyritic) |
fine-grained; may be porphyritic w/ feldspar, mica (biotite), hornblende or pyroxine (augite) |
associated with subduction zones |
medium (intermediate mafic; 55-65% silica) |
Na & Ca-plagioclase, amphibole, pyroxene (augite), mica (biotite) |
| Basalt (porphyritic, amygdaloidal, vesicular) |
fine-grained; fast-cooled, by atmosphere's cool temperature or by water |
non-viscous lava moving great distances |
dark (mafic) |
CA-plagioclase, pyroxene (augite), olivine, magnetite, apatite |
| Dacite |
fine-grained (cools too fast for minerals to grow); may be porphyritic |
light, med. (intermediate felsic) |
Na-pplagioclase, ambhibole, biotite mica, quartz |
|
| Rhyolite (also: banded) |
fine-grained (cools too fast for minerals to grow); may be porphyritic |
light, med. (intermediate felsic) |
quartz, orthocase, Na-plagioclase, mica (biotite) |
|
| Obsidian (also: snowflake) |
fine-grained; conchoidal fracture; glassy |
viscous acid lava; rapid-cool |
dark (mafic); silica-rich |
glass; phenocrysts of quartz and feldspar |
| Pumice |
fine-grained; vesicular;
low density (floats in water) |
lava, ash / volcanic
(frothy rhyolitic volcanic lava)
|
medium (intermediate felsic) |
|
| Scoria |
vesicular |
dark (mafic) |
Ca-plagioclase, pyroxene (augite), olivine |
|
| Tuff (lithic, crystal) |
fine-grained |
pyroclast / volcanic
(ash deposited in atmosphere)
|
medium (intermediate felsic) |
lithic, vitric, or crystal formations |
Send comments to Rob Viens (e-mail: rviens@bcc.ctc.edu) or call him at his Bellevue Community College office at (425) 564-3158. Office hours are by appointment.