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Mechanical and Chemical Weathering

Weathering is categorized as mechanical and chemical weathering. The former indicates that temperature and pressure changes cause rocks to disintegrate physically. On the other hand, the latter indicates that the mineral’s structure is altered by either the removal or addition of some elements due to chemical agents (Eastern Illinois University, n. d. ). List and describe the four main types of mechanical weathering and the three main types of chemical weathering discussed in the textbook. Mechanical weathering has four main types: frost wedging, mechanical exfoliation, abrasion, and thermal expansion.

Frost wedging means that water expands when it freezes, thus breaking rocks (Gore, 2004). Mechanical exfoliation means that rocks are exposed to exfoliation when they are exposed to lower confining pressure. Abrasion simply means that rocks rub against each other (Scarborough High School Geoscience, n. d. ). Thermal expansion involves heat and cooling causing the rocks to break (Gore, 2004). Chemical weathering has three types: hydrolysis, dissolution, and oxidation. Hydrolysis indicates the chemical reaction between water and other substances (Scarborough High School Geoscience, n.

d. ). Dissolution refers to the process where rocks are dissolved due to acidic waters (Eastern Illinois University, n. d. ). Oxidation refers to areas that have 21% oxygen in the atmosphere (Scarborough High School Geoscience, n. d. ). Of the three main types of sedimentary rocks (detrital, chemical, and organic), which of those are made-up of components almost entirely (if not entirely) derived from the mechanical weathering of preexisting rocks and/or minerals? Among the main types of sedimentary rocks, the detrital sediment was derived from pre-existing rocks.

The word ‘detrital’ means fragmented or broken grains California State Polytechnic University, n. d. ). One way to lithify sediments is to cement them together. This is typically done via one of three “gluing agents” (silica, calcite, or iron). Which type of weathering (mechanical or chemical) is responsible for the existence of these “gluing agents”? Chemical weathering is responsible for the formation of ‘gluing agents’ such as silicate, calcite, and iron. Lithification itself is a process reflecting chemical weathering. Lithification can occur through the precipitation of silica and calcium or oxidation of aluminum and iron.

Cementation is the process where precipitation of chemical cement from trapped water and circulating water. These ‘gluing agents’ can form as a result of chemical weathering. Silica, calcite, and iron are precipitate types that are chemical in nature (Pidwirny, 2006).

References

California State Polytechnic University. (n. d. ). Weathering and sedimentary rocks. Retrieved February 11, 2009, from http://geology. csupomona. edu/drjessey/class/Gsc101/Weathering. html Eastern Illinois University. (n. d. ). Mechanical and Chemical Weathering. Retrieved February 11, 2009, from http://www. ux1. eiu.

edu/~cfjps/1300/weathering. html Gore,P. J. W. (2004). Weathering of rocks and formation of sediment. Georgia Perimeter College. Retrieved February 11, 2009, from http://facstaff. gpc. edu/~pgore/geology/historical_lab/weathering. php Pidwirny, M. (2006). Characteristics of sedimentary rocks. Fundamentals of Physical Geography, 2nd Edition. Retrieved February 11, 2009, from http://www. physicalgeography. net/fundamentals/10f. html Scarborough High School Geoscience. (n. d) Weathering. Retrieved February 11, 2009, from http://www. scarborough. k12. me. us/high/projects/geoscience4/sbergg/erosion. htm

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