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Molten material that emerges at the earth's surface:
LAVA, cools to form VOLCANIC, or EXTRUSIVE igneous rock
a combination of melted silicate material, volatiles, and possible already solidified crystals
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)
igneous rocks rich in dark-colored ferromagnesian minerals (augite and hornblende) but with an abundant plagioclase feldspar
igneous rocks composed chiefly of dark-colored ferromagnesian minerals, especially olivine and augite, with no plagioclase feldspar
absence of crystals (frothy glassy) indicates-
extremely rapid cooling of lava with high dissolved gas content (see bubbles)
crystal size: porphyry
igneous rock with large crystals (phenocrystals) set in a matrix of finer-grained crystals (groundmass)
(deconstructional feature) following catastrophic emptying of a magma chamber , a large region collapses; i.e. Yellowstone Caldera, Wyoming
higher temperature magmas commonly have:
lower viscosity, lower volatile content, less explosive tendency (lava rather then pyroclastic material)
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