Rocks Classification PDF

Rocks Table of Contents Classifying Rocks Igneous Rocks Sedimentary Rocks Rocks from Reefs Metamorphic Rocks The Rock Cycle menu-exit menu-help menu-menu menu-arrow-L Rocks - Classifying Rocks Studying Rocks When studying a rock sample, geologists...

Rocks Table of Contents Classifying Rocks Igneous Rocks Sedimentary Rocks Rocks from Reefs Metamorphic Rocks The Rock Cycle menu-exit menu-help menu-menu menu-arrow-L Rocks - Classifying Rocks Studying Rocks When studying a rock sample, geologists observe the rock’s mineral composition, color, and texture. menu-exit menu-help menu-menu menu-arrow-L Rocks - Classifying Rocks Mineral Composition and Color Rock – a solid mixture of minerals and other materials. Rock-forming minerals – the common minerals that make up most of the rocks of Earth’s crust. – Granite – tends to be a light-colored rock that has high silica content – Basalt – tends to be a dark-colored rock that is low in silica menu-exit menu-help menu-menu menu-arrow-L Rocks - Classifying Rocks Texture Grains – particles of minerals or other rocks that give a rock its texture. Texture – the look and feel of a rock’s surface, determined by the size, shape, and pattern of a rock’s grains. menu-exit menu-help menu-menu menu-arrow-L Rocks - Classifying Rocks Texture Grain size – Coarse-grained – large easy to see grains – Fine-grained – so small they can only be seen under a microscope menu-exit menu-help menu-menu menu-arrow-L Rocks - Classifying Rocks Texture Grain Shape – varies greatly from sand grains to large triangular grains Grain Pattern – can vary also from layers to swirls to bands menu-exit menu-help menu-menu menu-arrow-L Rocks - Classifying Rocks How Rocks Form Geologists classify rocks into three major groups: – igneous rock, sedimentary rock, and metamorphic rock. menu-exit menu-help menu-menu menu-arrow-L Rocks - Classifying Rocks How Rocks Form Igneous rock – type of rock that forms from the melting then cooling of molten rock at or below the surface. Sedimentary rock – type of rock that forms when particles from other rocks or the remains of plants and animals are pressed and cemented together. Metamorphic rock – type of rock that forms from an existing rock that is changed by heat and pressure menu-exit menu-help menu-menu menu-arrow-L Rocks - Igneous Rocks Classifying Igneous Rocks Igneous rocks are classified according to their origin, texture, and mineral composition. menu-exit menu-help menu-menu menu-arrow-L Rocks Classifying Igneous Rocks Extrusive igneous rock – forms from lava on Earth’s surface. Intrusive igneous rock – forms when magma hardens beneath Earth’s surface. The faster igneous rock cools, the finer the grains – Extrusive igneous rock tends to be a finer- grained rock than intrusive igneous rock menu-exit menu-help menu-menu menu-arrow-L Rocks - Igneous Rocks Mineral Mixture Granite is a mixture of light-colored minerals, such as feldspar and quartz, and dark-colored minerals, including hornblende and different types of mica. But granite can vary in mineral composition. This affects its color and texture. menu-exit menu-help menu-menu menu-arrow-L Rocks - Igneous Rocks Mineral Mixture Reading Graphs: – What mineral is most abundant in granite? – Feldspar menu-exit menu-help menu-menu menu-arrow-L Rocks - Igneous Rocks Mineral Mixture Reading Graphs: – About what percentage of granite is made up of dark minerals? – 10% menu-exit menu-help menu-menu menu-arrow-L Rocks - Igneous Rocks Mineral Mixture Calculating: – If the amount of quartz increases to 35 percent and the amount of dark-colored minerals stays the same, what percentage of the granite will be made up of feldspar? – 100% - (35% + 10%) = 55% menu-exit menu-help menu-menu menu-arrow-L Rocks - Igneous Rocks Mineral Mixture Predicting: – How would the color of the granite change if it contained less feldspar and more mica and hornblende? – The overall color would be darker. menu-exit menu-help menu-menu menu-arrow-L Rocks Intrusive rock bodies Lacolith: Large mushroom- or dome-shaped intrusive body consisting of a dome- shaped sill and a smaller feeder dike menu-exit menu-help menu-menu menu-arrow-L Rocks Igneous composition and temperature Bowen’s reaction series: Progression of minerals that can crystallize as temperature decreases menu-exit menu-help menu-menu menu-arrow-L Rocks Discontinuous: discrete steps between mineral phases. Each one is entirely different Continuous: Plagioclase feldspars can have any amounts of calcium and sodium menu-exit menu-help menu-menu menu-arrow-L Rocks Fractionation Mafic minerals crystallize first—use up iron and magnesium and increase concentration of aluminum, potassium, and sodium. Both mafic and felsic rocks crystallized from a single melt containing all the major elements. menu-exit menu-help menu-menu menu-arrow-L Rocks Fractional Crystallization menu-exit menu-help menu-menu menu-arrow-L Rocks Intrusive rock bodies Dike: Sheet-like intrusive rock body that cuts across layering in surrounding rocks Mafic dike in the Grand Canyon, AZ (discordant) menu-exit menu-help menu-menu menu-arrow-L Rocks Intrusive rock bodies Sill: Sheet-like intrusive rock body that follows layering in surrounding rocks Sill (concordant) Big Bend, Texas menu-exit menu-help menu-menu menu-arrow-L Rocks Sedimentary processes Significance of sedimentary rocks -Provide a record of ancient tectonic events (e.g., mountain building and erosion) -Fossil record-evolution of life -Major reservoirs of groundwater, oil, coal -History of past climate changes menu-exit menu-help menu-menu menu-arrow-L Rocks Sedimentary Rocks Clastic Sediments – physically transported rock fragments produced from weathering of preexisting rocks, typically silicate minerals or rock fragments (quartz, feldspar, pyroxene, clays, rock fragments etc) - e.g. sandstone, shale Chemical and Biochemical Sediments – direct, chemical deposition (either by chemical reaction or biotic production), typically in marine settings (i.e. Oceans) - e.g. limestone, evaporite Chemical/Biochemical sediments can be eroded and transported to form a hybrid type. menu-exit menu-help menu-menu menu-arrow-L Rocks Mechanism of Sedimentary rocks 1. Weathering 2. Erosion 3. Transport 4. Sedimentation 5. Burial 6. Diagenesis menu-exit menu-help menu-menu menu-arrow-L Rocks - Sedimentary Rocks From Sediment to Rock Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation. menu-exit menu-help menu-menu menu-arrow-L Rocks - Sedimentary Rocks From Sediment to Rock Sediment – small, solid pieces of material that come from rocks or organisms. – Usually forms due to erosion Erosion – a destructive process in which water or wind loosens and carries away fragments of rock. Deposition – process by which sediment settles out of the water or wind that is carrying it. menu-exit menu-help menu-menu menu-arrow-L Rocks - Sedimentary Rocks From Sediment to Rock Compaction – process by which sediments are pressed together under their own weight. – Occurs over millions of years as layers build Cementation – process by which dissolved minerals crystallize and glue particles of sediment together into one mass. – Takes place when sediment is in the presence of water menu-exit menu-help menu-menu menu-arrow-L Rocks - Sedimentary Rocks Types of Sedimentary Rock There are three major groups of sedimentary rocks: – clastic rocks, organic rocks, and chemical rocks. Clastic rock – sedimentary rock that forms when rock fragments are squeezed together under high pressure. – Can range in size from microscopic clay particles to large boulders – Ex: shale, sandstone, conglomerate, and breccia menu-exit menu-help menu-menu menu-arrow-L  Categories of sedimentary rocks Rocks Clastic sedimentary rocks: Made up of rock and/or mineral fragments pressed and/or cemented together menu-exit menu-help menu-menu menu-arrow-L Rocks Clastic sedimentary rocks Direct relationship between the speed of current transporting sediment and the size of clasts (sediment particles) that can be moved—Faster current = larger particles menu-exit menu-help menu-menu menu-arrow-L Rocks Clastic sedimentary rocks Grain size says a lot about clastic sedimentary rocks and the environment of deposition Clastic sedimentary rocks named based on grain size menu-exit menu-help menu-menu menu-arrow-L Rocks Clastic sedimentary rocks Conglomerate: Particles are pebble-sized or larger—Rarely can be boulders the size of cars menu-exit menu-help menu-menu menu-arrow-L Rocks Clastic sedimentary rocks Sandstone: Sedimentary rock containing particles that are sand-sized Will feel rough, like sandpaper. menu-exit menu-help menu-menu menu-arrow-L Rocks Clastic sedimentary rocks Mudstone: Sedimentary rock containing particles that are mud-sized Particles too small to see with naked eye. menu-exit menu-help menu-menu menu-arrow-L Rocks - Sedimentary Rocks Types of Sedimentary Rock Chemical rock – sedimentary rock that forms when minerals crystallize from a solution. (Reacts to HCl) – Ex: Limestone forms from calcite deposits dissolved in lakes, rivers, streams. menu-exit menu-help menu-menu menu-arrow-L  Categories of sedimentary rocks Rocks Chemical sedimentary rocks: Made up of minerals precipitated from water, either directly or as the inorganic shells of living organisms menu-exit menu-help menu-menu menu-arrow-L Rocks Chemical sedimentary rocks Inorganic chemical sedimentary rocks: Precipitated directly from water Biogenic chemical sedimentary rocks: Accumulated shells of marine organisms (coral, sea shells, and exoskeletons of plankton) menu-exit menu-help menu-menu menu-arrow-L  Categories of sedimentary rocks Rocks Organic sedimentary rocks: Made up of accumulated organic matter menu-exit menu-help menu-menu menu-arrow-L Rocks - Sedimentary Rocks Types of Sedimentary Rock Organic rock – sedimentary rock Peat that forms from remains of organisms deposited in thick layers. – Ex: Coal and Limestone Lignite – Coal forms from the remains of swamp plants buried in water. – Limestone forms in the ocean, where Bituminous many living things, such as coral, clams, and oysters, have hard shells made of calcite that collect on the ocean floor. Anthracite menu-exit menu-help menu-menu menu-arrow-L Rocks Inorganic chemical sedimentary rocks Occur in arid environments with restricted water circulation—Great Salt Lake or the Dead Sea. menu-exit menu-help menu-menu menu-arrow-L Rocks Inorganic chemical sedimentary rocks Rock salt: Salt deposited by evaporation of salt lakes or sea water Salt on roads and sidewalks menu-exit menu-help menu-menu menu-arrow-L Rocks Inorganic chemical sedimentary rocks Rock gypsum: Rocks made up of a mineral called gypsum (calcium sulfate—CaSO4·2H2O) Deposited by evaporation of salt lakes or seawater Used to make drywall menu-exit menu-help menu-menu menu-arrow-L Rocks - Sedimentary Rocks Uses of Sedimentary Rock Sedimentary rock has been used for thousands of years in building structures, tools, and statues. – Ex: The White House in Washington D.C. is constructed of sandstone. menu-exit menu-help menu-menu menu-arrow-L Rocks Biogenic chemical sedimentary rocks Limestone: Rock made almost entirely of calcite (CaCO3) Shallow-water limestones made of coral and shells Deep-water limestones made of planktonic shells menu-exit menu-help menu-menu menu-arrow-L Rocks Biogenic chemical sedimentary rocks Chert: Rock made of microcrystalline silica from planktonic shells menu-exit menu-help menu-menu menu-arrow-L Rocks - Rocks From Reefs Coral Reefs Coral reef – a structure of calcite skeletons built up by coral animals in warm, shallow ocean water. – When coral animals die, their skeletons remain. More corals build on top of them, gradually forming a coral reef. – Only form in ocean water between 30°N and 30°S latitude menu-exit menu-help menu-menu menu-arrow-L Rocks Coral Reefs(not in notes) Coral reef is really organic(from living things) limestone. Deposits of organic limestone help geologists figure out what the environment was like long ago. If they find a fossil of coral reef, they would know that location used to contain warm, shallow ocean water. menu-exit menu-help menu-menu menu-arrow-L Rocks - Metamorphic Rocks Metamorphic Rock Metamorphic rock – forms when heat and pressure beneath Earth’s surface changes the appearance, texture, crystal structure, and mineral content of either igneous, sedimentary, or other metamorphic rock. menu-exit menu-help menu-menu menu-arrow-L  Rocks Metamorphic Processes Metamorphic Rock: A rock whose original mineralogy, texture and/or composition has changed due to pressure, temperature and/or fluids. Metasomatic Rock: A metamorphic rock whose whole bulk chemical composition was altered during interaction with fluids Metamorphism and deformation often go together menu-exit menu-help menu-menu menu-arrow-L Rocks Metamorphic Grade Refers to the intensity of metamorphism. High grade: High temperature and pressure Low grade: Low temperature and pressure menu-exit menu-help menu-menu menu-arrow-L Rocks Metamorphism Metamorphism: Transformation of solid rock in response to heat and pressure to form new minerals and textures menu-exit menu-help menu-menu menu-arrow-L Rocks Driving forces—Heat Heat due to igneous intrusions: Igneous intrusions heat up the rocks around them Area baked by an igneous intrusion called contact aureole Contact metamorphism Sill menu-exit menu-help menu-menu menu-arrow-L Rocks Heat due to igneous intrusions Felsic intrusions are ~700° C (1300° F) or more Mafic intrusions are ~1100° C (2000° F) or more For comparison: – Iron melts at 1538° C (~2800° F) – Aluminum melts at 660° C (~1220° F) Pottery kiln is metamorphism menu-exit menu-help menu-menu menu-arrow-L Rocks Heat due to igneous intrusions Amount of metamorphism around intrusion function of its size, its T, and the T of the surrounding rocks Metamorphism in southern Maine Gray = Igneous intrusive rocks Yellow–red = metamorphic rocks menu-exit menu-help menu-menu menu-arrow-L Rocks Types of metamorphism Contact metamorphism: Metamorphism generated by heat from intrusive rock bodies under static pressure conditions Often involves relatively high T’s and low P’s Localized in nature menu-exit menu-help menu-menu menu-arrow-L Rocks Limestone protolith Marble: Metamorphic rock that forms from limestone Contains calcite and/or dolomite—May also contain silicate minerals such as amphibole and pyroxene menu-exit menu-help menu-menu menu-arrow-L Rocks - Metamorphic Rocks Types of Metamorphic Rocks Geologists classify metamorphic rocks according to the arrangement of the Shale grains that make up the rocks. – Foliated rocks – metamorphic Slate rocks that have grains arranged in parallel layers or bands. Gneiss – Ex: Slate – metamorphic shale (denser and more compact than shale) menu-exit menu-help menu-menu menu-arrow-L Rocks - Metamorphic Rocks Types of Metamorphic Rocks Nonfoliated rocks – metamorphic rocks that have randomly arranged metamorphic grains that do not split into layers – Ex: Quartzite – metamorphic sandstone Marble – metamorphic limestone menu-exit menu-help menu-menu menu-arrow-L Rocks - The Rock Cycle A Cycle of Many Pathways Forces deep inside Earth and at the surface produce a slow cycle that builds, destroys, and changes the rocks in the crust. menu-exit menu-help menu-menu menu-arrow-L Rocks - The Rock Cycle Rock cycle – processes on the surface and inside Earth that slowly change rocks from one kind to another. menu-exit menu-help menu-menu menu-arrow-L Rocks - The Rock Cycle The Rock Cycle and Plate Tectonics Plate movements start the rock cycle by helping to form magma, the source of igneous rocks. Plate movements also cause faulting, folding, and other motions of the crust that help to form sedimentary and metamorphic rocks. menu-exit menu-help menu-menu menu-arrow-L Rocks - The Rock Cycle Rock Cycle Magma Metamorphic Igneous Sedimentary menu-exit menu-help menu-menu menu-arrow-L Rocks Graphic Organizer Rocks can be Igneous Sedimentary Metamorphic include include include Non- Intrusive Extrusive Clastic Organic Chemical Foliated foliated menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks menu-exit menu-help menu-menu menu-arrow-L Rocks Q&A menu-exit menu-help menu-menu menu-arrow-L