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Thread: From Granite to mud

  1. #1 From Granite to mud 
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    Dec 2008
    Explain the surface process by which material that originated in grainte may eventually accumulate as a mud.
    Weathering, erosion, transportation and deposition (750 words)

    So far I have:

    Granite, an igneous rock is formed deep within the Earth and cooled very slowly, to contain large crystals; quartz, white feldspar and mica.

    Physical weathering, heating & cooling produce forces in the rock, expansion & contraction stress the rock. Eventually the forces begin to split the mineral form each other allowing water to seep along the grain boundaries. Freezing and thawing then liberates the grains. Once it's broken up, chemical weathering gets to grips on the surfaces. The main processes of chemical weathering are acids and oxidation, which often operate together. As rainwater dissolves carbon dioxide it is slightly acidic, this attacks the minerals in the rock. The feldspars and the micas are very susceptible to chemical weathering. The quartz is very resistant to chemical weathering.
    During weathering, hydrogen ions break free their loosely bonded metal atoms. When this happens the structure collapses to form clay minerals.
    The minerals are exposed to flowing water that lead to erosion. The grains as they are carried away pound, blast and scrape more debris to wear away the surface when they pass. The grains are also broken down as they move along to become smaller and more rounded.

    Transportation of grains or sediment depends on the energy supplied by the transporting system and the size of the grains. Large grains settle to the stream bed, smaller grains roll or bounce along the stream bed and even smaller grains are picked up and carried along in suspension. The grains are also exposed to physical abrasion and chemical attack. Reactive minerals form clay minerals and dissolved ions while quartz is liberated. The transported grains eventually collide with the stream bed and each other. The rock fragments tend to become rounded by the abrasion, rather than broken by impact due to the water cushioning the impacts.


    Thats about it. For deposition should I talk about currents, flow rates etc, degree if sorting?
    Also should I add more detail to above? like chemical equations, examples?
    I think my main problem is refering it to mud.

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  3. #2  
    WYSIWYG Moderator marnixR's Avatar
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    Apr 2007
    Cardiff, Wales
    you could try and address how the different components (quartz, felspar and plagioclase) behave during erosion / transportation, and how different compositions of granite can affect this process

    don't know whether the following site helps : Weathering and Granite Landscapes: Case Study - DARTMOOR

    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  4. #3  
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    Jan 2007
    Good andwer so far I'd say, but it could perhaps be expanded on a bit.

    I'd say you need to talk about transport and deposition a tad more. The question asks specifically about mud. What kind of conditions and environments lead to the deposition of such a fine sediment as opposed to a gravelly or sandy deposit which can also come from granite? What portions of the original rock will this mud mostly consist of?

    You've also only mentioned water transport. I don't know if you'll be expected to deal with mass movement, glaciation or wind transport.
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  5. #4  
    Forum Senior Booms's Avatar
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    Sep 2008
    The perceptual schematic known as earth
    simply explore all possible methods for the rock to end up in mud, talk about how the larger grains in the silt bed are broken up by water erosion and what happens to the shards of rock that are brushed off as the grains are rounded in the water

    you could take it down the biological ingestion route animals,plants take up water with the grains in, use it and pump some of the material out as gases and waste and use others, the life dies and rots into compost, which is further broken down into mud by plants and rain, while the gas and waste is taken by other animals and so on and so forth
    It's not how many questions you ask, but the answers you get - Booms

    This is the Acadamy of Science! we don't need to 'prove' anything!
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  6. #5  
    Universal Mind John Galt's Avatar
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    Jul 2005
    It is a good effort. I would largely agree with the other poster's remarks, but here are a couple of additional points.

    1. Feldspar, not white feldspar. Many granites contain pink orthoclase.
    2. You should note that most of the quartz grains, because they are resistant to chemical and physical attack, are large and do not form an important constituent of the mud. Therefore you will be focusing on the fine, suspended clay particles.
    3. On that basis discussion of sorting need only address the fact that clays will settle out only when current flow is almost zero, which occurs either some distance from the river mouth, or on flood plains after a flood.
    4. Your reference to freezing/thawing is only accurate in temperate zones. Granites in the tropics also weather. You need to discuss that.

    I wasn't quite sure what you meant about the problem of referring to it as mud.
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