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28 terms

Chapter 6

Lab Note: Certain slides need to be studied that may not be included in this set list
STUDY
PLAY
igneous rocks
formed by the crystallization (or solidification) of melted material
Molten material that emerges at the earth's surface:
LAVA, cools to form VOLCANIC, or EXTRUSIVE igneous rock
Molten material within the earth:
MAGMA. cools to form PLUTONIC, or INTRUSIVE igneous rock
Magma
a combination of melted silicate material, volatiles, and possible already solidified crystals
Volatiles
substances (chiefly water) that are gases at low temperatures
Viscosity
resistance of a substance to flow; examples: pine sap (higher) vs. water (lower); increases as the lava starts to cool; the more complex the silicate melted in the magma, the higher the viscosity (complex: quartz, orthoclase)
classification of igneous rocks
mineral composition and texture
felsic
igneous rocks rich in light-colored minerals as orthoclase and quartz
intermediate
igneous rocks rich in minerals such as Na-Ca plagioclase and hornblende
mafic
igneous rocks rich in dark-colored ferromagnesian minerals (augite and hornblende) but with an abundant plagioclase feldspar
ultramafic
igneous rocks composed chiefly of dark-colored ferromagnesian minerals, especially olivine and augite, with no plagioclase feldspar
absence of crystals (dense glassy) indicates-
extremely rapid cooling of lava (quenching)
absence of crystals (frothy glassy) indicates-
extremely rapid cooling of lava with high dissolved gas content (see bubbles)
large crystals indicate-
slow cooling
pegmatic texture indicates-
slow cooling in the presence of water
crystal size: fine grained
less then 1 mm
crystal size: medium grained
1-2 mm
coarse-grained
larger then 2 mm
crystal size: porphyry
igneous rock with large crystals (phenocrystals) set in a matrix of finer-grained crystals (groundmass)
plutonic rock body
sill, dike, batholith
volcanic landform
fissure flow, shield volcano, composite volcano
crater
(constructional feature) volcanic material accumulates at the surface; i.e. Mt. Rainier
caldera
(deconstructional feature) following catastrophic emptying of a magma chamber , a large region collapses; i.e. Yellowstone Caldera, Wyoming
mafic magma
typically has a higher temperature than felsic magma
higher temperature magmas commonly have:
lower viscosity, lower volatile content, less explosive tendency (lava rather then pyroclastic material)
pyroclastic rock
explosively erupted as hot but nevertheless solid particles
tuff
explosively erupted, fine-grained volcanic rock whose grains are commonly welded together
vesicles
cavities in volcanic rocks, once occupies by gas bubbles