<p> Earth Materials- Rocks</p><p>Three types of rocks: </p><p>1) Igneous : formed from liquid-crystal mush- magma 2) Metamorphic: formed at high Temp. and Pressure 3) Sedimentary: formed at surface of earth</p><p>Igneous rocks</p><p>Classified according to 1) mineral composition and 2) texture or grain size.</p><p>Two main types: 1) Plutonic or intrusive and 2) volcanic or extrusive.</p><p>Plutonic (intrusive) rocks are coarse grained, volcanic (extrusive) rocks are fine grained- different rates of cooling</p><p>Examples of intrusive (plutonic) igneous rocks: Granite, Diorite, Gabbro</p><p>Examples of extrusive (volcanic) rocks: Rhyolite, andesite, basalt.</p><p>The rock pairs granite- rhyolite, diorite-andesite, gabbro-basalt have the same chemical composition, but different texture (i.e. grain size).</p><p>When a magma cools, low silica (SiO2 or quartz), and high Fe and Mg silicate minerals crystallize first: olivine and pyroxene (also called mafic minerals).</p><p>Last silicate minerals to crystallize are high silica (SiO2 or quartz) and high K minerals: Quartz and feldspar and mica (also called felsic minerals). </p><p>Volcanic rocks include: lava flows and pyroclastic rocks. Sedimentary rocks</p><p>3 types: clastic, chemical and biogenic</p><p>1) clastic: composed of fragments of preexisting rocks. Classified according to grain size: clay < silt < sand < gravel.</p><p>Clay lithifies to shale Silt lithifies to siltstone Sand lithifies to sandstone Gravel lithifies to conglomerate</p><p>2) Chemical: chemically precipitated from water: e.g. limestone (CaCO3), rock salt (NaCl), gypsum (CaSO4).</p><p>3) Biogenic: formed from fossilized living material: </p><p>Coal from dead plant material (trees etc), </p><p>Chert from dead SiO2-rich shells, Chalk form CaCO3-rich shells </p><p>In general all sedimentary rocks characterized by layering or stratification.</p><p>Cross-bedding – formed by wind or flowing water. Mud-cracks – drying out of sediment by sun.</p><p>Metamorphic rocks</p><p>Produced by high temperatures and pressures in Earth</p><p>Characterized by Foliation: parallel alignment of minerals.</p><p>Foliation is a plane of weakness in metamorphic rocks</p><p>Metamorphic equivalents Shale = Slate, Schist Limestone = marble</p><p>Quartz sandstone = quartzite</p><p>Granite = Gneiss (pronounced nice) </p><p>Gneiss is a coarse grained foliated metamorphic rock</p><p>Rock cycle: all three rock types can be converted to each other by common geologic processes (see Fig. 2,12 text) .</p>