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Lithification Sediments Deposition Transport Erosion Weathering Sedimentary Rocks From Sediment to Rock • Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation. Weathering The sediments that make up sedimentary rocks are produced by: Mechanical & Chemical Weathering Mechanical Weathering Chemical Weathering Mineral Stability Products of Weathering • Lithic (Rock) Fragments (granite, basalt, schist, etc.) • Dissolved Ions (Calcium, Potassium, Sodium, etc.) • Rust Minerals (Hematite, Goertite, etc.) • Clay Minerals (Bentonite, Montmorillonite, etc.) • Residual Minerals (Quartz, Orthoclase, Muscovite, etc.) Erosion & Transport Water Wind Ice Gravity Deposition Lithification Sediment Rock Cementation Typical Cement: •Calcite •Quartz Sedimentary Rocks Identification Note: Use the same terms to describe sediments & sedimentary rocks. Only difference is lithification! Rock Identification is based on: • Composition What minerals make up the rock? • Texture What is the shape, size and orientation of the mineral grains that make up the rock? Major Difference: Crystalline vs. Clastic Types of Sedimentary Rocks Detrital Rocks Chemical Rocks vs. Difference: Texture Detrital (Clastic Texture) vs. Chemical (Crystalline Texture) Detrital Rock Composition Detrital Rocks • Lithic Fragments • Quartz • Clay Minerals • Fossil Fragments • Rust Minerals • Orthoclase • Muscovite / Biotite Detrital Rock Texture Clastic Texture • Grain Size • Grain Sorting • Grain Rounding • Sediment Maturity Grain Size •Gravel 2mm •Sand 1/16 mm •Mud - Silt 1/256 mm •Mud - Clay Detrital Rock Names (Based Primarily on Grain Size) Gravel Sized: Conglomerate Sand Sized: Sandstone Mud Sized: Mudstone Siltstone Shale Sorting Grain Roundness Gravel Sized Detrital Rocks (Subdivided Based on Grain Roundness) Conglomerate Breccia Maturity Mature •Well Sorted •Well Rounded •All Quartz Immature •Poorly Sorted •Angular grains •Mixed Composition including clay Quartz Sandstone Lithic Sandstone Arkose (Sandstone) Sandstones (Subdivided based on maturity) Greywacke Sandstones Under a Scope Detrital Sedimentary Rock ID Clastic (Detrital) Sedimentary Rocks Grai n Size Roundne ss Sorting Composi tion Name Rounded Moderate to poor Fragme nts of any rock type CONGLOMER ATE Angular Moderate to poor Fragme nts of any rock type BRECCIA Rounded Well All Quartz - usually white to tan QUAR TZ SANDSTO NE Subrounded to Angular Moderate to poor (few grains >2mm) Feldspar (usually orthoclase), micas, quartz, and other minerals ARKO SE (Arkosic Sandstone) Subrounded Moderate to well Quartz, lithic fragments, and other mine rals LITHI C SANDSTO NE Rounded to angular Moderate Quartz and rock fragments mixed with >15% clay; often gray colored GRAYWA CK E SANDSTO NE (to small to see) Well Clay and quartz (but usually too small to see) SILTSTONE Clay (but usually too small to see); Massive MUDS TONE Clay (but usually too small to see); Breaks into semi-flat layers SHALE Gravel-sized (> 2 mm) Sand-sized (visible grains up to 2 mm) Silt-sized (feels gritty) Clay-sized (feels smooth) (to small to see) Well Chemical Rock Texture Crystalline Texture • Coarse • Fine Chemical Sedimentary Rocks (Names based primarily on composition) Composition • Calcite • Quartz (silica) • Halite • Gypsum • “Carbon” / Plant Remains Basic Rock Name • Limestone • Chert • Rock Salt • Rock Gypsum • Peat or Coal Chemical Rocks (Names based mainly on composition) Limestones Crystalline Limestone Fossiliferous Limestone Chalk Chemical Rocks (cont.) Evaportites Chert Rock Salt Rock Gypsum Coal Chemical Sedimentary Rock ID Chemical, Biochemical & Organic Sedimentary Rocks Composi tion Calcite (acid reaction) Dolomite (acid reaction) Texture Name Crystalline - medium to coarse (visible) grains CRYST ALLINE LIMESTONE Crystalline - grains too small to see MICR ITE Abundant fossils in a fine- to coarse-grained crystalline matrix FOSSILIFEROUS LIMESTONE Fine-grained powder, earthy smell (often black, gray, or white) CHA LK Crystalline - fin e to coarse grained DOLOSTONE Quartz (scratches glass) Crystalline - grains too small to see; conchoidal fracture CHE RT Fine-grained powder, earthy smell (no acid reaction) (often white) DIA TOMIT E Gypsum Crystalline - fin e to coarse grained ROCK GYPS UM Halite (tastes salty) Crystalline - fin e to coarse grained ROCK S ALT Fibrous, brownish plant material; soft PEAT Dense, black masses; depending on grade may be dull to vitreous; lower gra des may contain minor fossils COAL Plant Remains (Carbon) Sedimentary Rocks on Earth