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MINERALS AND ROCKS IN THE EARTH’S CRUST Igneous, Sedimentary, Metamorphic Rocks and Environments MINERALS AND ROCKS COME FROM ELEMENTS • Chemical elements are the fundamental materials of which all matter is composed. – From the modern viewpoint: • a substance that cannot be broken down or reduced further MAKING MINERALS FROM ELEMENTS • ALMOST ALL THE MINERALS FOUND IN THE EARTH ARE FORMED FROM THE BONDING OF EIGHT (8) ELEMENTS – OXYGEN (O) MOST ABUNDANT – SILICON (Si) – ALUMINIUM (Al) – IRON (Fe) – CALCIUM (Ca) – POTASSIUM (K) – SODIUM (Na) LEAST ABUNDANT – MAGNESIUM (Mg) WHAT ARE MINERALS? • BUILDING BLOCKS FOR ROCKS • DEFINITION: – NATURALLY OCCURRING, – INORGANIC SOLIDS, – CONSISTING OF SPECIFIC CHEMICAL ELEMENTS, AND – A DEFINITE ATOMIC ARRAY • CRYSTALLINE STRUCTURE – ‘CRYSTAL’ • ‘CRYSTAL’ AND ‘MINERAL’ INTERCHANGEABLE TERMS MINERALS Minerals divided into two main groups based on Silica content Silica (SiO) compound of molecularly bonded silicon (Si) and oxygen (O) molecules (SiO, SiO2, SiO4, SiO6 etc.) GROUP 1: SILICATES – CONTAIN SILICA GROUP 2: NON-SILICATES (CONTAIN NO SILICA) NON-SILICATE MINERALS • Non-silicate minerals are very rare • Make up 5% of Earth’s continental crust – Considered valuable commercially as building materials, gemstones, iron ores for steel, ceramics, and more. • Native metals: gold, silver, copper, platinum • Native elements: diamonds, corundum: Ruby (red) or Sapphire (blue) • Carbonates: calcite (used in cement) • Oxides: hematite (iron ores) • Sulfides: galena (lead ores) • Sulfates: gypsum (used in plaster, dry wall) • Halides: halite (table salt) SILICATE MINERALS • THE MOST ABUNDANT OF ALL MINERALS – MAKE UP APPROXIMATELY 95% OF WEIGHT OF EARTH’S CRUST – CONTAIN VARYING AMOUNTS OF SILICA (SiO) • DOMINANT COMPONENT OF MOST ROCKS: – IGNEOUS – SEDIMENTARY – METAMORPHIC SILICATE MINERALS • LISTED BELOW IN DECREASING % OF SILICA ARE MOST COMMON SILICATE MINERALS – QUARTZ (SiO2) (“High” Silica content ~100%) – FELDSPARS (PLAGIOCLASE – MICAS (MUSCOVITE – BIOTITE ) – AMPHIBOLES (Hornblende) – PYROXENES (Augite) – OLIVINE (“Low” Silica content ~40%) SILICATE MINERALS • SILICATE MINERALS ARE BROKEN INTO THREE MAIN GROUPS ACCORDING TO % SILICA – FELSIC – MAFIC – ULTRAMAFIC High percent Low percent FELSIC SILICATE MINERALS • FELSIC SILICATE MINERALS HAVE A HIGH CONCENTRATION OF SILICON, OXYGEN, ALUMINIUM AND POTASSIUM • FELSIC SILICATES – HIGH % SiO (75100%) – QUARTZ (100% SiO2) – FELDSPARS (Plagioclase, Orthoclase) – MUSCOVITE MICA QUARTZ FELDSPAR MUSCOVITE MICA MAFIC SILICATE MINERALS • MINERALS WITH HIGH CONCENTRATION OF MAGNESIUM AND IRON, PLUS CALCIUM AND SODIUM, AND LOWER AMOUNTS OF SILICON AND OXYGEN • MAFIC SILICATES - LESS SiO (50-60%) – BIOTITE MICA – AMPHIBOLE (Hornblende) – PYROXENE (Augite) BIOTITE MICA PYROXENE (AUGITE) AMPHIBOLE (HORNBLENDE) ULTRAMAFIC SILICATES • MINERALS WITH GREATER CONCENTRATION IN MAGNESIUM AND IRON. VERY RARE AT EARTH’S SURFACE • ULTRA MAFIC SILICATES - VERY LOW % SiO (less than 50%) • VERY RARE AT SURFACE – OLIVINE (FORSTERITE, FAYALITE) WHAT ARE ROCKS? • AGGREGATIONS OF 2 OR MORE MINERALS – Same or different minerals combine together • THREE CATEGORIES – IGNEOUS – SEDIMENTARY – METAMORPHIC IGNEOUS ROCKS • Ignis: Latin for “Fire” • FORMED FROM MOLTEN MATERIAL THAT COOLED AND SOLIDIFIED AT, NEAR, OR DEEP BELOW, THE SURFACE • TYPES: – PLUTONIC (INTRUSIVE) –IGNEOUS ROCKS COOLED AND SOLIDIFIED BELOW SURFACE AT GREAT DEPTHS – VOLCANIC (EXTRUSIVE) – IGNEOUS ROCKS COOLED AND SOLIDIFIED AT OR NEAR THE SURFACE THROUGH VOLCANIC ERUPTIONS IDENTIFICATION OF IGNEOUS ROCKS • TWO IDENTIFICATION PROCESSES FOR PLUTONIC OR VOLCANIC IGNEOUS ROCKS: – TEXTURE: • Size, shape and manner of growth of individual crystals – MINERAL COMPOSITION • Based on SiO content – Felsic, Intermediate, Mafic – (high Silica low Silica) TEXTURE IDENTIFICATION • SIZE, SHAPE OF CRYSTALS AND MANNER OF GROWTH • FINE GRAINED TEXTURE: – VERY TINY, MINERAL CRYSTALS VISIBLE ONLY WITH MAGNIFICATION – INDICATES FAST COOLING AT SURFACE – CRYSTALS SOLIDIFIED QUICKLY WITH NO TIME TO ‘GROW’ • COARSE-GRAINED TEXTURE: – LARGE, EASILY-VISIBLE MINERAL CRYSTALS – INDICATES SLOW COOLING AT DEPTH – CRYSTALS SOLIDIFIED SLOWLY WITH LOTS OF TIME TO ‘GROW’ TEXTURE IDENTIFICATION Fine-Grained Textures Coarse-Grained Textures MINERAL COMPOSITION • CLASSIFIED BY SILICA (SiO) CONTENT • FELSIC – MORE THAN 85% SILICA • INTERMEDIATE – 60-85% SILICA • MAFIC – LESS THAN 60% SILICA COMMON IGNEOUS ROCKS • FELSIC IGNEOUS ROCKS (>85% SiO) – GRANITE: • PLUTONIC-INTRUSIVE; COARSE-GRAINED TEXTURE; FELSIC MINERAL COMPOSITION – RHYOLITE: • • VOLCANIC-EXTRUSIVE; FINE-GRAINED TEXTURE; FELSIC MINERAL COMPOSITION INTERMEDIATE IGNEOUS ROCKS (60-85% SiO) – DIORITE: • PLUTONIC-INTRUSIVE; COARSE-GRAINED TEXTURE; INTERMEDIATE MINERAL COMPOSITION – ANDESITE: • VOLCANIC-EXTRUSIVE; FINE-GRAINED TEXTURE; INTERMEDIATE MINERAL COMPOSITION • MAFIC IGNEOUS ROCKS (<60% SiO) – GABBRO: • PLUTONIC-INTRUSIVE;COARSE-GRAINED TEXTURE; MAFIC MINERAL COMPOSITION – BASALT: • VOLCANIC-EXTRUSIVE; FINE-GRAINED TEXTURE; MAFIC MINERAL COMPOSITION IGNEOUS ROCK IDENTIFICATION CHART Granitic Andesitic Basaltic (Felsic) (Intermediate) (Mafic) Coarse-Grained Granite Diorite Gabbro Fine-Grained Rhyolite Andesite Basalt Rock color based on % mafic minerals Light-colored <15% mafic minerals Medium-colored 15-40% mafic minerals Dark grayblack >40% mafic minerals Viscosity Highest Medium Low Melting Temps 600-8000 C 800-11000 C 1 100-12000 C FELSIC IGNEOUS ROCKS RHYOLITE VOLCANICEXTRUSIVE PLUTONICINTRUSIVE GRANITE INTERMEDIATE IGNEOUS ROCKS VOLCANICANDESITE EXTRUSIVE DIORITE PLUTONICINTRUSIVE MAFIC IGNEOUS ROCKS GABBRO BASALT VOLCANICEXTRUSIVE PLUTONICINTRUSIVE OTHER IGNEOUS ROCKS • VOLCANIC GLASS: – OBSIDIAN: VOLCANIC-EXTRUSIVE; NO CRYSTALS FORM; SILICA-RICH, COOLED INSTANEOUSLY – PUMICE: VOLCANIC-EXTRUSIVE; NO CRYSTALS FORM; SILICA-RICH; SOLIDIFIED FROM ‘GASSY’ LAVA • PYROCLASTIC ROCKS – TUFF: VOLCANIC-EXTRUSIVE; SOLIDIFIED ‘WELDED’ ASH VOLCANIC GLASS OBSIDIAN PUMICE PYROCLASTIC IGNEOUS ROCKS WELDED TUFF SEDIMENTARY ROCKS • WEATHERING PROCESSES BREAK ROCK INTO PIECES, SEDIMENT. • HOW SEDIMENTATION HAPPENS : – TRANSPORTATION DEPOSITION BURIAL AND LITHIFICATION INTO NEW ROCKS. SEDIMENTARY PROCESSES • LITHIFICATION: • As sediment is buried several kilometers beneath the surface, heated from below, pressure from overlying layers, heat, and chemically-active water converts the loose sediment into solid sedimentary rock • Compaction - volume of a sediment is reduced by application of pressure • Cementation - sediment grains are bound to each other by materials originally dissolved during chemical weathering of preexisting rocks – typical chemicals include silica and calcium carbonate. CLASSIFYING SEDIMENTARY ROCKS • THREE SOURCES FOR SEDIMENTARY ROCKS • (1) Detrital (or clastic) sediment is composed of transported solid fragments (or detritus) of pre-existing igneous, sedimentary or metamorphic rocks • (2) Chemical sediment forms from previously dissolved minerals that either precipitated from solution in water, or were extracted from water by living organisms • (3) Organic sedimentary rock consisting mainly of plant remains CLASTIC/DETRITAL SEDIMENTARY ROCKS • CLASSIFIED ON GRAIN OR PARTICLE SIZE • Shales: finest-grained • Sandstones: medium-grained • Conglomerates – Breccias: coarsegrained SHALES : CLASTIC SEDIMENTARY • SHALES: finest-grained clastic sedimentary rocks – composed of very small particles – 50% of all sedimentary rocks are Shales – Consist largely of Clay minerals (weathered granite in many cases) – Subcategories: Claystones – Siltstones Mudstones – Economic value: building material; china and ceramics; spark plug housings SHALES Burgess Shale in Canada Limestone on black shale MUDSTONES, SILTSTONES Identified by decreasing amounts of sand and increasing amounts of clay SANDSTONES • SANDSTONES: medium-grained clastic sedimentary rocks • 25% of all sedimentary rocks fall into this category • Economic value: glass; natural reservoirs for oil, gas, and groundwater SANDSTONES CONGLOMERATES - BRECCIAS • CONGLOMERATES AND BRECCIAS: • The coarsest of all the clastic sedimentary rocks • Composed of particles >2 mm in diameter – Conglomerate - the particles are rounded – Breccia - the particles are angular CONGLOMERATES BRECCIAS CHEMICAL SEDIMENTARY ROCKS • TWO CATEGORIES: – INORGANIC CHEMICAL SEDIMENTARY – ORGANIC CHEMICAL SEDIMENTARY INORGANIC CHEMICAL SEDIMENTARY ROCKS • Formed when dissolved products of chemical weathering precipitate (‘form out of’) from solution • Most common types: – Inorganic limestones and cherts: precipitates directly from seawater and fresh water – Evaporites: precipitates when ion-rich water evaporates INORGANIC - LIMESTONES • Limestones - account for 10% - 15% of all sedimentary rocks formed from Calcite or Calcium Carbonate (CaCO3). • Formed as pure carbonate muds accumulate on the sea floor • Also formed on land: – Tufa - a soft spongy inorganic limestone that forms where underground water surfaces – Travertine - forms in caves when droplets of carbonate-rich water on the ceiling, walls and floors precipitate a carbonate rock: stalactites and stalagmites LIMESTONES TRAVERTINE Tufa Towers, Mono Lake ORGANIC LIMESTONES • Formed with calcite from marine environment: CaCO3 shells and internal/external skeletons of marine animals • Coquina - “crushed” shell fragments cemented with CaCO3 • Chalk - made from billions of microscopic carbonatesecreting organisms • Coral Reefs - Formed from the skeletons of millions of tiny invertebrate animals who secrete a calcite-rich material. Live “condo” style while algae acts as the cement to create the large structures called “reefs”. • Organic Chert - formed when silica-secreting microscopic marine organisms die (radiolaria {single-celled animals} and diatoms {skeletons of singled-celled plants}) • Flint - an example of an Inorganic Chert COQUINA, CHALK AND FOSSILIFEROUS LIMESTONES COQUINA FOSSILIFEROUS LIMESTONE CHALK ORGANIC SEDIMENTARY ROCKS • Coal - Organic sedimentary rock consisting mainly of plant remains • Formation: – Burial of decaying vegetation; – Increasing pressure from the overlying layers expels water, CO2 and other gases; – Carbon accumulates. • STAGES: • Peat - formed early in the process, when the original plant structure can still be distinguished. • Lignite - a more hardened form of Peat • Bituminous - more pressure and more heat produce this moderately hard coal. • Anthracite - the hardest coal - formed from metamorphic processes under extreme heat and pressure - Hard - Shiny - the most desired as an energy resource. COAL PEAT LIGNITE ANTHRACITE BITUMINOUS SEDIMENTARY ENVIRONMENTS • • • • • • • • Lakes Lagoons Rivers Ocean bottoms Estuaries Salt Flats Playas Glacial environments METAMORPHIC ROCKS • METAMORPHISM : process by which conditions within the Earth alter the mineral content and structure of any rock - igneous, sedimentary or metamorphic without melting it. • Metamorphism occurs when heat and pressure exceed certain levels, destabilizing the minerals in rocks...but not enough to cause melting • Ion-rich fluids circulating in and around rocks also influences metamorphism METAMORPHIC PROCESSES • HEAT: – (2000 C or 4000 F) reached near 10 km (6 miles) beneath the surface. • PRESSURE: – > 2 bar or 2000 mb, which is generally found ~ 6 km (4 miles) beneath the Earth’s surface • FLUIDS: Chemicallyactive water is the usual fluid and comes from various sources TEMPERATURE/PRESSURE For every 3 kilometers depth in the Earth, pressure increases by about 1 kb. Average temperature gradient in the Earth increases 30° C per km CHANGES IN METAMORPHIC ROCKS • Metamorphic processes cause many changes in rocks – Increased density – Growth of larger crystals – FOLIATION : reorientation of the mineral grains into layers or banded texture – Transformation of low-temperature minerals into high-temperature minerals CLASSIFYING METAMORPHIC ROCKS • TEXTURE: the size, shape and distribution of particles in a rock – texture is determined by grade of metamorphism • Low grade: (less than 6000C and lower than 4 kilobars pressure) • Intermediate grade: occurs at a variety of temperatures and pressures. • High grade: (greater than 6000C and more than 4 kilobars pressure) FOLIATED TEXTURES • Foliated texture: more pressure and mineral grains realign themselves and grow into larger crystals • Three types of foliated texture: – Slaty Texture (Low grade metamorphism) – Schistosity (Medium grade metamorphism) – Gneissic Texture (High grade metamorphism) ROCK – SLATY TEXTURE SLATE • Shale metamorphosed to Slate: – clay minerals become unstable and recrystallize into mica crystals – Slate is formed under Low-Grade Metamorphism SLATE SCHISTOCITY - SCHIST • More extreme pressures and temperatures: mica crystals grow even larger - ~ 1 cm in diameter. – rock has “scaly” appearance - schistosity, – referred to as a Schist. • Schists formed under Intermediate-Grade Metamorphism • Schists named for the mineral constituents in the parent rock: – mica schist – talc schist – garnet schist SCHIST Mica schist Ruby schist GNEISSIC TEXTURE - GNEISS • Light and dark silicate minerals separate and re-align themselves into bands • Rocks with this texture are called Gneiss • Gneiss forms from High Grade Metamorphism • Typical ‘parent’ rocks for Gneiss – – – – granite diorite gabbro shale GNEISS NON-FOLIATED TEXTURES • Rocks with only one mineral metamorphose without a visibly foliated texture • Limestone metamorphoses into Marble as the interlocking calcite crystals grow larger • Quartz Sandstone metamorphoses into Quartzite MARBLE AND QUARTZITE MARBLE QUARTZITE METAMORPHIC ENVIRONMENTS • CONTACT METAMORPHISM – Metamorphism of a rock touched by the intense heat of migrating magma. • REGIONAL METAMORPHISM – Burial metamorphism - occurs when rocks are overlain by more than 6 miles of rock or sediment – Dynamothermal metamorphism - occurs when rocks are caught between two convergent plates during mountain building Contact and Regional Metamorphism Regional Metamorphism Contact Metamorphism ROCK FORMING PROCESSES THE ROCK CYCLE