Chapter 3, 11th ed. I. Rock cycle A. Shows the interrelationships among the three rock types B. Earth as a system: the rock cycle 1. Magma a. Crystallization 2. Igneous rock a. Weathering b. Transportation c. Deposition 3. Sediment a. Lithification 4. Sedimentary rock a. Metamorphism 5. Metamorphic rock a. Melting 6. Magma C. Full cycle does not always take place owing to "shortcuts" or interruptions;; for example,, 1. Sedimentary rock melts 2. Igneous rock is metamorphosed 3. Sedimentary rock is weathered 4. Metamorphic rock weathers II. Igneous rocks A. Form as magma cools and crystallizes 1. Rocks formed inside Earth a. Called plutonic or intrusive rocks 2. Rocks formed on the surface a. Formed from lava (a material similar to magma, but without gas) b. Called volcanic or extrusive rocks B. Crystallization of magma 1. Ions arrange themselves into orderly patterns 2. Crystal size is determined by the rate of cooling a. Slow rate produces large crystals b. Fast rate produces microscopic crystals c. Very fast rate produces glass C. Classification is based on the rock's texture and mineral constituents 1. Texture a. Size and arrangement of crystals b. Types 1. Fine-grained—fast rate of cooling 2. Coarse-grained—slow rate of cooling 3. Porphyritic (two crystal sizes)—two rates of cooling4. Glassy—very fast rate of cooling 2. Mineral composition a. Explained by Bowen's reaction series, which shows the order of mineral crystallization b. Influenced by crystal settling in the magma D. Nomenclature of igneous rocks 1. Granitic rocks a. Composed almost entirely of light-colored silicates—quartz and feldspar b. Also referred to as felsic: feldspar and silica (quartz) c. High silica content (about 70 percent) d. Common rock is granite 2. Basaltic rocks a. Contain substantial dark silicate minerals and calcium-rich plagioclase feldspar b. Also referred to as mafic: magnesium and ferrum (iron) c. Common rock is basalt 3. Other compositional groups a. Andesitic (or intermediate) b. Ultramafic III. Sedimentary rocks A. Form from sediment (weathered products) B. Constitute about 75 percent of all rock outcrops on the continents C. Used to reconstruct much of Earth's history 1. Contain clues to past environments 2. Provide information about sediment transport 3. Often contain fossils D. Economic importance 1. Coal 2. Petroleum and natural gas 3. Sources of iron and aluminum E. Classification of sedimentary rocks 1. Two groups based on the source of the material a. Detrital rocks 1. Material is solid particles 2. Classified by particle size 3. Common rocks are a. Shale (most abundant) b. Sandstone c. Conglomerate d. Siltstone b. Chemical rocks 1. Derived from material that was once in solution and precipitated to form sediment a. Directly precipitated as the result of physical processes b. Precipitated through life processes (biochemical origin) 2. Common sedimentary rocksa. Limestone—the most abundant chemical rock 1. Coquina 2. Chalk 3. Travertine c. Microcrystalline quartz (precipitated quartz) 1. Chert 2. Flint 3. Jasper 4. Agate d. Evaporites 1. Rock salt 2. Gypsum e. Coal 1. Lignite 2. Bituminous F. Produced through lithification 1. Loose sediments are transformed into solid rock 2. Lithification processes a. Compaction b. Cementation by 1. Calcite 2. Silica 3. Iron oxide G. Features 1. Strata, or beds (most characteristic) 2. Bedding planes separate strata 3. Fossils a. Contain traces or remains of prehistoric life b. Are the most important inclusions c. Help determine past environments d. Are used as time indicators e. Are used for matching rocks from different places IV. Metamorphic rocks A. Rocks that have changed form B. Produced from preexisting 1. Igneous rocks 2. Sedimentary rocks 3. Other metamorphic rocks C. Metamorphism 1. Takes place where preexisting rock is subjected to temperatures and pressures unlike those in which it formed 2. Degrees of metamorphism a. Exhibited in the rock's texture and mineralogy b. Types 1. Low-grade (e.g., shale becomes slate) 2. High-grade (causes the original features to be obliterated)D. Metamorphic settings 1. Contact, or thermal, metamorphism a. Near a mass of magma b. Change is driven by a rise in temperature 2. Regional metamorphism a. Result of directed pressures and high temperatures during mountain building b. Produces the greatest volume of metamorphic rock E. Metamorphic agents 1. Heat 2. Pressure (stress) a. From burial (confining pressure) b. From differential stress during mountain building 3. Chemically active fluids a. Mainly water and other volatiles b. Promote recrystallization by enhancing ion migration F. Metamorphic textures 1. Foliated texture a. Minerals in a parallel alignment b. Minerals perpendicular to the compressional force 2. Nonfoliated texture a. Contains equidimensional crystals b. Resembles a coarse-grained igneous rock G. Common metamorphic rocks 1. Foliated rocks a. Slate 1. Fine-grained 2. Splits easily b. Schists 1. Strongly foliated 2. "Platy" 3. Types based on composition (e.g., mica schist) c. Gneiss 1. Strong segregation of silicate minerals 2. "Banded" texture 2. Nonfoliated rocks a. Marble 1. Parent rock—limestone 2. Large, interlocking calcite crystals 3. Used as a building stone 4. Variety of colors b. Quartzite 1. Parent rock—quartz sandstone 2. Quartz grains are fused V. Resources from rocks and minerals A. Metallic mineral resources1Gold, silver, copper, mercury, lead, and others 2. Concentrations of desirable materials are produced by a. Igneous processes b. Metamorphic processes 3. Most important ore deposits are generated from hydrothermal (hot-water) solutions a. Contain metal-rich fluids b. Associated with cooling magma bodies c. Types of deposits include 1. Vein deposits in fractures or bedding planes 2. Disseminated deposits distributed
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