Geology Lab Week 4 Notes and readinng
Geology Lab Week 4 Notes and readinng GEOS 1111L
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This 3 page Class Notes was uploaded by Brandon Notetaker on Monday September 19, 2016. The Class Notes belongs to GEOS 1111L at University of Arkansas taught by Josh Stokes in Fall 2016. Since its upload, it has received 7 views. For similar materials see Geology Lab in Geology at University of Arkansas.
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Date Created: 09/19/16
Week 4 Lab and Reading Assignment (Week of 9/11/16) Igneous Rocks Rocks which have crystallized from molten rock Composed of different minerals Lava Extrusive (Volcanic) Molten rock above ground Magma Intrusive (Plutonic) Molten rock underground Igneous Rock Textures Textures refer to crystalline structure; governed by cooling rate; affects size or organization Phaneritic Intrusive (Plutonic) Large, Coarse Crystals Slow Cooling Aphanitic Extrusive (Volcanic) Fine Grained Crystals Fast Cooling Polyphyritic Multiple Crystal Sizes Multiple Cooling Stages Special Igneous Rock Textures Volcanic Textures refer to crystalline structure; governed by cooling rate; size or organization Glassy Extrusive (Volcanic) Unorganized Crystals Fast Cooling Obsidian, Pumice Vesicular Extrusive (Volcanic) Porous due to gas Fine Grained Crystals Fast Cooling Pumice, Scoria Pyroclastic Tuffaceous – fragments < 4mm Volcanic Breccia – fragments > 4mm Classifying Igneous Rocks Mineral Composition Quartz Crystalline, Many Colors Orthoclase Cleavage, Pink Plagioclase Cleavage, White Amphibole (ferromagnesian) DarkGreen to Black Augite (ferromagnesian) Brown, Black, Greenish, VioletBrown Olivine (ferromagnesian) Green Crystals Classifying Igneous Rocks Mineral Composition Felsic Abundant Quartz, Orthoclase > Plagioclase, < 15% ferromagnesian, Granite Intermediate Little to No Quartz, Plagioclase > Orthoclase, 15 – 40% ferromagnesian, Diorite Mafic No Quartz or Orthoclase 10 – 60% Plagioclase 40 – 90% ferromagnesian – Gabbro Identifying Igneous Rocks Mineral Texture – Phaneritic, Aphanitic, Porphyritic, Glassy, Vesicular, and Pyroclastic Mineral Composition Is There Quartz? Plagioclase or Orthoclase? and Ferromagnesian Minerals Classifications – Felsic, Intermediate, and Mafic Chapter 5 – Reading Assignment Pages 8791: What is the definition of a sedimentary rock? What are the two processes that create sedimentary rocks? Understand the types of sedimentary rocks created from these processes. Sedimentary Rocks – Consist of a material derived from preexisting rocks through physical erosion and chemical weathering. Two processes that create sedimentary rocks Physical Erosion – erosion of rocks by wind and water to produce solid particles such as clay silt, sand, and pebbles (Which can become cemented together to form detrital sedimentary rock) Chemical weathering – alternation of rocks by water to produce chemical elements in solution and (commonly) residual clay. There can be either the complete dissolving of rock, or partial dissolving of minerals, putting some elements in solution and leaving others behind as a residue of clay minerals that comprise soil Detrital – fragments produced through disintegration. Elements in solution precipitated? Organic sedimentary rocks – Skeletal remains of plants and animals Chemical – precipitated directly from water Lithification – myriad processes where different materials contribute to development of sedimentary rocks. Four processes (Compaction, Cementation, Precipitation, and Recrystallization) Detrital Sedimentary Rocks Classified by sizes of grain. Gravel – Grains are pebble size Sand – Grains range from the size of match heads down to pinhead. sandpaper Silt – Grains are hardly visible to the unaided eye, but abrasive to touch like the fine side of a nail file. Gritty to the teeth Clay – Not abrasive. Smooth. Slick when wt. pasty to the teeth. Mud – a mixture of silt and clay Breccia – pebble size grains are angular in shape. Organic Sedimentary Rocks Two kinds: Organic limestones and organic carbon Organic Limestones – consist of fragments of sea shell cemented together. 3 common varieties (Fossiliferous, Coquina, and Chalk) Organic Carbon – Coals consist of organic carbon residue of plants that were buried with sediments and later compacted and distilled by the heat and pressure of burial. Chemical Sedimentary Rocks Two Groups: primary and secondary Primary chemical sedimentary rocks – precipitated on rock surfaces and in open spaces within rocks at or near Earth’s surface. Includes Rock Salt, Rock gypsum, and Chemical limestone. Secondary Chemical Sedimentary rock – develops through the chemical change of earlier rock by elements transported by water. Includes Dolostone, and Chert (flint) Rock Salt – Evaporite mineral that is precipitated within seas and lakes where water has evaporated to a salinity approximately ten times saltier than that of seawater. Rock gypsum – precipitated within seas and lakes where water has evaporated to a salinity approximately four times that of seawater Chemical limestone – calcium carbonate that is precipitated Dolostone – rock that consists of dolomite produced by the replacement of limestone by the activity of magnesium in water. Chert (flint) – Rock that consists of microcrystalline quartz. Pages 9295, 98100: Familiarize yourself with the Table 5.1, and notice the different sedimentary structures on pg. 99.
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