GEOG - Lecture 17 Review

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Texas Tech University *

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1401

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Geology

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Oct 30, 2023

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Review 17 17 Rocks and Weathering 17.1 Rocks Mineral – A naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition crystal form, and physical properties. Intrusive igneous Rocks – Forms when magma is trapped deep inside the Earth - Great globs of molten rock rises toward the surface Extrusive igneous – Igneous rocks produced when magma exists and cools above (or very near) the Earth’s surface. - Rocks that form at erupting volcanoes and oozing fissures Clastic Sed. Rocks – Made up of prices (clasts) or pre-existing rocks. - Pieces of rocks loosened by weathering, then transported to some basin or depression where sediment is trapped. - If sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock. Chemical Sed. Rocks – A type of rock that begins as sediments, which are then cemented together through natural processes. - Start out as a solution of water, ions, and sediment and are formed via the evaporation of water and the precipitation of ions over time. Chemical Precipitates – Formation of a separation solid substance from a solution, either by converting the substance into an insoluble form or by changing the composition of the solvent to dimmish the solubility of the substance in it. Evaporites – Rocks precipitated from saturated surface or near-surface brines by hydrologies driven by solar evaporation. Organic Sed. Rocks – Those containing large quantiles of organic molecule. - Contain carbon Metamorphic rocks – Rocks that started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form. Regional Metamorphism – A type of metamorphism in which the mineralogy and texture of rocks are changed over a wide area by deep burial and heating associated with the large-scale forces of plate tectonics.

Contact Metamorphism – A type of metamorphism where rock minerals and texture are changed, mainly by heat, due to contact with magma. Rock Cycle – The processes through which the three main rock types (igneous, metamorphic, and sedimentary) transform from one type into another. 17.2 Weathering Chemical Weathering – The process of chemicals in rainwater making changes to the minerals in a rock. Physical Weathering – The process that breaks rocks apart without changing their chemical composition Chemical stability – The thermodynamic stability of a chemical system Factors affecting chem. Weathering – Temperature, surface area, and available water. Hydrolysis – The chemical breakdown of a compound due to reaction with water. Oxidation – A process in which a chemical substance changes because of the addition of oxygen Exfoliation – Separation of successive thin shells, or spalls, from massive rock such as granite or basalt. - Common in regions that have moderate rainfall Frost action – The process of alternate freezing and thawing of moisture in soil, rock and other materials, and the resulting effects on materials and on structures placed on, or in, the ground. Salt crystal growth – Repeated tidal cycles lead to growth of salt crystals until they begin to press against the sides of cracks or pores, exerting tensional pressure. 17.3 Relation Between Chemical and Physical Weathering Relation between chem. & phys. weathering

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