Chemical weathering is more common and occurs faster in tropical regions, due to heat and abundant water from rain. All of these chemical processes lead to increased weathering of rocks. Hydrolysis of alkali feldspar, or orthoclase, can also result in the formation of kaolinite and other substances. Chemical weathering, via hydrolysis of feldspar, also makes the very common clay minerals and quartz. In hydrolysis, minerals change when exposed to acidic water to make solutions, such as saltwater solution. In dehydration, water is removed from rock, such as when water is removed from limonite to form hematite. Hydration also leads to rock deformation. Water changes anhydrite to gypsum in this way. In hydration, the actual chemical bonds of a rock will change from the absorption of water. Rust presents as the classic reddish-orange color in iron. (CC-BY-2.5 Lobineau).Oxidation is a type of chemical weathering in which rocks with iron content will react with oxygen and water, leading to rust. 5.S: Weathering, Erosion, and Sedimentary Rocks (Summary).The study of depositional environments is a complex endeavor. Knowing where and how a particular sedimentary rock was formed can help geologists paint a picture of past environments-such as a mountain glacier, gentle floodplain, dry desert, or deep-sea ocean floor. 5.5: Depositional Environments The ultimate goal of many stratigraphy studies is to understand the original depositional environment.Below is a summary discussion of common sedimentary structures that are useful for interpretations in the rock record. They use uniformitarianism to usually compare sedimentary structures formed in modern environments to lithified counterparts in ancient rocks. Geologists use these structures to interpret the processes that made the rock and the environment in which it formed. 5.4: Sedimentary Structures Sedimentary structures are visible textures or arrangements of sediments within a rock.Chemical rocks are classified mainly by the composition of minerals in the rock. Geographical features may include lakes, rivers, streams. Chemical sedimentary rocks are precipitated from water saturated with dissolved minerals. The definition of topography is the shape, size, and arrangement of geographical features of the Earths surface in a given location. They are classified by grain shape, grain size, and sorting. Clastic rocks may also include chemically weathered sediment. Clastic or detrital sedimentary rocks are made from pieces of bedrock, sediment, derived primarily by mechanical weathering. 5.3: Sedimentary Rocks Sedimentary rock is classified into two main categories: clastic and chemical. Chemical weathering includes carbonic acid and hydrolysis, dissolution, and oxidation. Mechanical weathering includes pressure expansion, frost wedging, root wedging, and salt expansion. Weathering is a process that turns bedrock into smaller particles, called sediment or soil. 5.2: Weathering and Erosion Bedrock refers to the solid crystalline rock that makes up the Earth’s outer crust.Several special properties make water an especially unique substance, and integral to the production of sediments and sedimentary rock. It also is a weathering and erosion agent, producing the grains that become detrital sedimentary rock. It is one of the main agents involved in creating the minerals in chemical sedimentary rock. 5.1: The Unique Properties of Water Water plays a role in the formation of most sedimentary rocks.
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