The Rock Cycle11/26/2014°Sedimentary Rocks°-Rock that forms at or near the surface of the Earth in one of several ways: by the cementing together of loose clasts (fragments or grains) produced by physical or chemical weathering of preexisting rock; by the growth of sell masses or the cementing together of shells and shell gragments; by the accumulation of subsequent alteration of organic matter from dead plankton or plants; or by the precipitation of minerals from water solution. °°Weathering and Sedimentary Rocks°-The combination of processes that break up and corrode solid rock, eventually transforming it into sediment. °°Physical Weathering°-Breaks intact rock into unconnected grains and chunks. °1) Root wedging(as discussed in class): as roots grow, they apply pressure to their surroundings, and can push joints open. °-This physically causes material to tumble down. °-Force open cracks, and cause blocks of material to fall down. °°2) Frost wedging: °-Freezing water busts popes and shatters bottles because water expands when it freezes and pushes the walls of the container apart. °-The same phenomenon happens in rock.°-When the water trapped in a joint freezes, it forces the joint open and may cause the joint to grow (force them apart). °-Ice occupies more space that liquid water. °°3) Sahara dessert (sand)°-Wind storms picks up sand grains and blasts particles against outcrop and break off tiny pieces of rock. °-You can physically weather rock (erode flat) with wind (high velocity).
°°4) Glacial action bringing about erosion°-Go down a river valley, carve river valley, pluck off pieces of rock fromthe sides of the river valley.°-It will polish the material underneath (the glacier has rock particles at the base, the rock particles grind over the underlying rock, polishing it, and also plucking out material. °-If you’re making a scratch, you’re eroding the rock. °°*Where would you expect physical weathering?°-Dry environment, and cold temperatures (a lot of time in the deep freeze)°°Chemical Weathering°-Refers to the many chemical reactions that alter or destroy minerals when rock comes in contact with water solutions and/or air. °-In the picture: indentations, it appears that the rock has been dissolved (not an effect of mechanical weathering). °*Where would you expect chemical weathering (environments)?°-will be maximized when its hot and humid (high rainfall and heat)Why is heat important? Chemical reactions go quicker at high temperature. °°°°Relative weathering rates of granite and marble°-Both gravestones were erected at the same time and place
°-The one on the left is marble, right granite. The marble one has eroded rapidly because its been exposed to acid.