Geology Chapter 4 Key Terms Lava- magma that reaches earth’s surface Extrusive/volcanic- igneous rocks that form when molten rock solidifies at the surface Intrusive/plutonic-igneous rocks that form from crystallization at depth Melt-liquid portion of magma Volatiles-gaseous components of magma Crystallization-slowing of ions that eventually join together into orderly crystalline structures • Silicon and oxygen link together first Factors that Affect Crystal Size 1. Rate at which the magma cools 2. Amount of silica present 3. Amount of dissolved gasses in the magma Glass- rocks that consist of unordered ions Aphanitic-igneous rocks that form at the surface, rapid cooling=very fine-grained texture Phaneritic-igneous rocks that solidify far below the surface, exhibit a coarse-grained texture Porphyritic-large crystals embedded in a matrix of smaller crystals • Large crystals in a porphyritic texture= phenocrysts • Matrix of smaller crystals= groundmass Pyroclastic- rocks formed from the consolidation of individual that rock fragments ejected from a volcano
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Granite, Felsic igneous, rich plagioclase feldspar, Rhyolite II