GEOL 101 Lecture Notes - Lecture 4: Igneous Rock, Feldspar, Extrusive Rock
11 Jan 2017
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Document Summary
Intrusive (plutonic: crystallized from slowly cooling magma intruded within the crust, rocks formed by intrusion of magmas into pre-existing country rock. Extrusive (volcanic: crystallized from rapidly cooling magma extruded on the surface, rocks formed by the cooling of pyroclastic material (fragments erupted into the air) Texture: the sizes and shapes of a rock"s minerals and their arrangement. High in si02 silica low in fe, mg iron and magnesium. Moderate in sio2 silica moderate in fe, mg iron and magnesium. Low in silica high in fe, mg. Very low in silica very high in fe, mg. Some minerals crystallize in an ordered series, while plagioclase feldspar crystalizes, from calcium-rich, sodium-rich form. Porphyritic crystals start to grow beneath earth"s surface. Melting temperature is controlled by water content, pressure and rock composition. Partial melting creates magma of a particular composition. A basaltic magma chamber breaks through, mixing results in andesitic magma.
