Igneous Rocks Ch3
From Ch3 Notes
Terms
undefined, object
copy deck
- Pumice
- Felsic to intermediate. Glassy froth (foam). Gray to white. Very light weight, often floats in water. Forms from explosive eruption of gas-saturated magma froth.
- Geothermal Gradient
- Rate of temp rise as depth increases. Very important to magma formation. Magma is most likely to form where the gradient is high.
- Plutonic
- Formed underground (also called intrusive). slow cooling = visible crystals.
- Pyroclastic
- Made of explosively ejected particles that are compressed and cemented, or welded.
- Volcanic
- fast cooling = fine grained or glassy textures
- Intermediate
- Nearly equal amounts of light (intermediate feldspar) and dark (ferromagnesian) minerals.
- Magman
- Forms deep underground - lower crust and upper mantle where temperatures are high enough to melt rock.
- Upward Movement of Magma
- Once formed, magma tends to rise because it is less dense than solid rock. It does this by: Pushing, Melting, Quarrying, Moving through open fractures or vents (fastest).
- Diorite
- Intermediate (medium dark). Roughly = mix of gray and/or white and black. 2nd most common plutonic rock.
- Magma
- Mostly water vapor (70%), carbon dioxide (20%) and sulfur dioxide.
- Granite
- Felsic (mostly light colored minerals). Typically pink or white with small % of dark minerals. Most common continental plutonic rock.
- Obsidian
- Usually felsic despite dark color. Solid glassy rock. Black, brown, or green due to tiny dark impurities. Sometimes translucent or even clear (no impurities).
- Andesite
- Intermediate. Fine-grained crystalline. Medium gray. Common lava in volcanic island arcs and continental volcanic arcs.
- Gabbro
- Mafic (dark). Dark gray, greenish gray, or black. Least common continental plutonic rock, but common in oceanic crust.
- Glassy
- Made of volcanic glass. Cooled too fast to form crystals.
- Basalt
- Mafic. Fine-grained crystalline. Dark gray to black. Often has gas bubbles. Most common lava. Upper ocean crust is basalt.
- Rhyolite
- Felsic. Fine-grained crystalline. Pink, purple, or light gray. Least common lava.
- Fine-Grained Crystalline
- Made of crystals too small to see.
- Igneous Rocks
- Rocks formed when molten rock (magma/lava) cools and solidifies.
- Coarse-Grained Crystalline
- Made entirely of visible (sparkling) crystals.
- Volcanic Rock
- Textures vary, but all have some fine-grained or glassy components.
- . Felsic
- Mostly light colored minerals - potassium feldspar, sodium feldspar and quartz, with a small % of ferromagnesians.
- Quarrying
- Magma intrudes cracks wedging out rocks that sink into it.
- Tuff
- Felsic to intermediate. Pyroclastic rock made of tiny ash particles that have been compressed & cemented or heat welded. Gray to white. Typically layered. Forms from explosive eruptions.
- Plutonic Rock
- All are coarse-grained (visibly) crystalline due to slow cooling deep underground.
- Ultramafic
- Mostly or entirely ferromagnesians, i.e. olivine, pyroxene, and garnet. Rare in the crust. Mantle is entirely this composition.
- Mafic
- Mostly or entirely dark minerals - calcium feldspar, and ferromagnesians (45-85%).
- Volcanic
- Formed on the surface (also called extrusive).