GEOL 110 - Minerals, Igneous Rocks Minerals Diamond Azurite Quartz Why Study Minerals?! Rocks = aggregates of minerals! Importance to Society?! Importance to Geology? 5 part definition, must satisfy all 5 parts! Naturally occurring - formed by nature Synthetic bismuth - Not a mineral Mineral - Rhodocrosite Granite with three minerals labeled! Inorganic - not organic (C-based) chemical! Solid - not liquid or gas Mussel shell is composed of aragonite, a mineral (controversial) Living part of mussel (inside shell) is organic and not a mineral. Liquid water is not a mineral Ice is solid (mineral) 1
! Definable chemical composition - can specify types and proportions of elements (mineral chemical formula) Quartz (SiO 2 ) Calcite (CaCO 3 )! Crystal structure - Orderly arrangement of atoms! Crystal structure controls shapes of crystal faces (flat shiny surfaces that form if mineral grows into open space)! Glass has random atomic arrangement (amorphous) Crystal structure of halite (NaCl) also known as salt. Halite crystals Mineral Identification! Definitive way = determine chemical composition and crystal structure but NOT usually done that way! Usually distinct set of physical properties allows mineral identification (fast and cheap) " Hardness " Luster " Cleavage Physical Properties of Minerals " Reaction with acid " Many others Mineral Physical Properties - Hardness! Resistance to scratching; soft mineral is easily scratched, hard mineral is difficult scratch! Talc is softest mineral, diamond is hardest! Quartz is relatively hard, calcite is relatively soft Mineral Physical Properties - Cleavage! Tendency of mineral to break along flat surfaces due to weak bonding; flat surfaces = cleavage faces! Examples of Cleavage: " One direction Mica " Two directions at 90º Feldspar Quartz is harder than glass Quartz is harder than calcite " Three directions NOT at 90º Demonstration - Calcite and Quartz hardness vs. steel knife 2
Luster! Way the mineral surface reflects light! Main categories = metallic, nonmetallic! Nonmetallic has many subdivisions, glassy is common Mineral Physical Properties-Reaction with Acid! Calcite fizzes, calcite dissolves releasing CO 2 gas CaCO 3 + H +! Ca 2+ + H 2 O + CO 2 (gas) Dolomite (CaMg(CO 3 ) 2 ) reacts more slowly with acid, only if powdered (small grains react quicker than large grains) Demo - Calcite reaction with acid Pyrite - metallic luster Quartz (left) and feldspar (right) - non-metallic and glassy luster Types of Minerals - Silicates Silicates - Quartz (SiO 2 )! Minerals are classified by chemical composition and crystal structure! Silicates - Most common in rocks and Earth (95% of Earth s crust); Contain silicon (Si) and oxygen (O)! Hard ( knife), glassy luster, no cleavage, variable color (commonly smoky gray or clear) Silicates - Feldspar! Hard ( knife), 2 cleavage planes (90 ), **rectangular crystals**, can be white to gray (plagioclase feldspar) or salmon color (K-feldspar) Mafic Silicates (Mg and Fe-rich)! Amphibole, Olivine, Pyroxene - usually dark color, various other properties Pyroxene Amphibole Olivine 3
Carbonates (contain CO 3 ) - Calcite, Dolomite! Calcite (CaCO 3 ) - Soft ( knife), bubbles vigorously in acid, 3 cleavage planes (rhombohedron = pushed over cube), white, gray, or colorless! Dolomite (CaMg(CO 3 ) 2 ) - Same as calcite, except bubbles in acid only if powdered Rock Definition Rock = coherent, relatively hard, naturally formed mass of mineral matter Calcite Dolomite Importance of Rocks Natural Hazards - Volcanoes, sinkholes, landslides direct link; Flood, EQ damage related to bedrock type Natural Resources - Rock, energy (fossil fuel), groundwater Rock Characterization Rocks are characterized based on: 1) Mineral content 2) Texture - size (large = coarse-grained; small, microscopic = fine-grained), shape, arrangement of mineral grains (aligned or random). Geologic History Igneous Rock Definition, Intrusive vs. Extrusive Form by cooling and solidification of hot molten rock Slow cooling below Earth's surface (intrusive igneous rock) produces large (coarse) mineral grains Fast cooling at Earth's surface (extrusive igneous rock) produces small (fine) mineral grains Fine-grained Igneous Rock Texture interlocking with random arrangement, no space between grains, similar to jigsaw puzzle Coarse-grained 4
Igneous Rock Classification 1) Texture - Coarse vs. fine-grained 2) Composition - mineral or chemical, color of rock (% light vs. dark minerals); Silicic = light rock, SiO 2 -rich, abundant quartz, feldspar; Mafic = dark rock, less SiO 2, rich in mafic (Mg, Fe-rich) silicates Igneous Rock Classification Bold = most important information for GEOL 110 Texture Composition Silicic Light color; abundant quartz, feldspar Coarse-grained Fine-grained 1) Granite 2) Rhyolite Intermediate Diorite Andesite Mafic Dark color; abundant Mg, Fe-silicates 3) Gabbro 4) Basalt Silicic Mafic Igneous Rock - Environment of Formation Granite, Gabbro Rhyolite Silicic or mafic magma cooled slowly deep in Earth (intrusion) Cooled quickly during explosive ash-flow volcanic eruption (high gas pressure) or after lava flow eruption (low gas pressure) Campus Building Stones - Rock Identification I) Sculpture Garden (along Mathews Ave., between Medical Sciences + Roger Adams Lab) Texture (grain size, shape, arrangement) Composition (minerals, chemical) Basalt Cooled quickly after lava flow eruption Rock Class (igneous, sedimentary or metamorphic) Rock Name Architectural Advantages Campus Building Stones - Rock Identification II) Burrill Hall (southwest side near entrance) Lower Area Texture (grain size, shape, arrangement) Composition (minerals, chemical) Rock Class (igneous, Sedimentary or metamorphic) Rock Name Architectural Advantages 5