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49 Cards in this Set
- Front
- Back
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What is weathering?
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A Pervasive phenomenon that alters rocks and minerals so that they are more nearly in equilibrium with a new set of environmental conditions
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What are the five factors of soil formation?
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Parent materials (rocks, sediments)
climate Vegetation slope time |
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How do organisms contribute to weathering?
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Burrowing animals (worms, rodents) constantly mix soil and sediment particles and bring material from depth to surface. Holes created allow water and air to depths. The roots of plants wedge themselves into cracks in rocks.
Plants remove ions from soil water and reduce the chemical stability of soil minerals, and plant roots release organic acid |
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Why do different rocks weather at different rates?
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the rate of chemical weathering proceeds depends on many different factors: the presence or absence of fractures, particle size, climate, parent material.
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What are the main products of weathering?
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physical weathering_ sediemnt and increased surface area
chemical weathering_clay minerals, ions in solution, residual quartz |
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What are clay minerals?
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Clay minerals are hydrous aluminium silicate, sometimes with variable amounts of iron, magnesium. Clays have structures similar to the micas and therefore form flat hexagonal sheets.
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What are the main soil horizons?
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A,E, B, C, R
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What are the main properties of soil horizon A?
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Intense weathering, Organic matter, dark color, clays and chemically stable minerals (ie: quartz)
"topsoil" |
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What are the main properties of soil horizon E?
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Leached zone
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What are the main properties of soil horizon B?
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"subsoil"
products of weathering accumulate, clay, red oxides |
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What are the main properties of soil horizon C?
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un-weathered sediment
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What are the main properties of soil horizon R?
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Un-weathered rock "bedrock"
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What is oxidation?
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The combination of oxygen with some other positively charged atom. most oxidation takes place in water with dissolved oxygen.
Iron + Oxygen = Iron oxide (Hematite) |
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What is hydolysis?
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weathering of silicate minerals.
Liberates soluble compounds and iron that may be oxidized. |
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What is dissolution?
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non-silicate minerals are involved.. its just dissolving things in water... you have to make the water slightly acidic
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How does physical weathering happen?
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Takes place when physical forces break minerals and rocks into smaller pieces that retain the composition of the parent material. The processes include frost wedging, unloading and exfoliation, and the activities of organisms.
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What is frost wedging?
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The growth of ice crystals in the cracks of rocks
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What is unloading and exfoliation?
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When a rock gets rid of the extra pressure it had when it was underground
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How does physical weathering contribute to chemical weathering?
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For example, cracks exploited by mechanical weathering will increase the surface area exposed to chemical action. Furthermore, the chemical action at minerals in cracks can aid the disintegration process.
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What are the climatic controls on physical and chemical weathering?
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chemical processes proceed more rapidly at high temperatures and in the presence of liquids. In addition, in hot, wet climates the processes of weathering can extend to the depths of several tens of meters as opposed to the few centimeters in arid and arctic regions.
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What are expansive soils? Why are they a problem?
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Expansive soils contain clay minerals that expand when wet and shrink when dry. Such volume changes damage structures such as foundations, roadways, and sidewalks.
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What are the main differences between forest soils and prairie soils in the Denton area?
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Sandstone_sandy forest soils, "cross timbers" vegetation
Carbonate rocks_Calcareous soils, expansive clay problem, prairie vegetation. |
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What are the main controls on erosion?
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the agents of currents such as, wind, water, or ice by downward or down-slope movement in response to gravity or by living organisms.
the amount and intensity of precipitation, the texture of the soil, the gradient of the slope, ground cover from vegetation, rocks, land use, and possibility of erosion from speed of a stream. |
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How can we control erosion and soil loss?
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Terracing, strip-cropping, crop rotation, contour plowing, no-till planting, windbreaks
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what is a depositional environment?
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The products of weathering (particles, ions, compounds in solution) are eroded from their original site and transported some distance. The geologic area where transportation ceases and the sediment is deposited is called a depositional environment.
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What do rounding and sorting reveal about clastic sediments?
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reveals how liquids and/or various pollutants move through rocks. Reveal transport and depositional history.
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How are sediments lithified?
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compaction reduces the volume of a deposit by decreasing the amount of pore space as particles fit more closely together. Cementation takes place when minerals crystallize in pore spaces and effectively bind the sedimentary particles to one another.
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What are the 3 most common cements in sedimentary rocks?
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Quartz, Calcite, Hematite
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What is the relationship between clastic sediment texture and transportation distance and energy?
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Good sorting means high energy, poor sorting means intermittent.
Angular grain shape means short transport, round mean long-term abrasion. |
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Why is quartz the most common mineral in sandstone?
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quartz is hard to weather
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How do carbonate rocks form?
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When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures.
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What is meant by the term "bioclastic"?
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rocks containing organic remains
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What are the most common evaporitic minerals?
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Gypsum, Halite
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What is the chemical formula for gypsum?
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CaSO4 * H2O
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What is the chemical formula for Halite?
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NaCl
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What is a sedimentry facies?
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Bodies of sediment with distinctive physical, chemical, and biological attributes.
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What do sedimentary structures tell us?
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Abrupt changes indicate either rapid changes in the type of sediment deposited or a period of deposition followed by nondepsition and then renewed deposition.
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How is lignite formed and where can we find it in TX?
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Formed by the accumulation of organic matter plus a rapid, shallow burial, compaction and "low cooking"...
found in the lignite mine in East Texas. |
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Why are sedimentary rocks so important economically?
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Many seidments and sedimentary rocks are important natural resources. Petroleum and natural gas as well as placer deposits of gold and diamonds are found in sedimentary rocks, as is most of the world's iron.
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What is metamorphism?
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the transformation through recrystallization of preexisting rocks inside Earth and is closely linked to plate tectonics
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How does metamorphism happen?
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Minerals seek to adjust to changing conditions in ways that maximize their stability. These may involve chemical reactions that change the mineral composition of a rock. Metamorphic fluids, which are very active in Earth's crust, greatly influence the ease with which certain mineral reactions take place. The absence of fluids and the loss of heat prevents retrograde metamorphic reactions from undoing the effects of metamorphism when erosion exposes these rocks to surface conditions.
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What are the tectonic settings of metamorphism?
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Andes-type mountain building (high heat & high pressure)
Contact (intense heat & low pressure) |
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What is regional metamorphism?
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involves heat and pressure and is associated with Andean-type mountain building
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What is contact metamorphism
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heat is the dominant agent driving contact metamorphism, which is restricted to the vicinity of igneous intrusions at shallow levels in the crust, where llithostatic pressure is the dominant type of pressure acting on the rock.
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What are the four textures of foliated rocks?
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slaty clevage, schistosity, gneissic texture
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What are the most common non-foliated rocks?
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marble and Quartzite
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Why do metamorphic rocks occur in zones of similar grade?
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Determined on presence of key minerals
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Where can we see metamorphic rocks in TX?
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Can find Gneiss in Llan and Van Horn
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What are some economic uses of metamorphic rocks and minerals?
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yeild products of value in ordinary construction, art, metallurgy, jewelry, and cultural expression
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