Tomorrow we have another exam. The main focus of this week was different kinds of rocks: metamorphic, igneous, and sedimentary. Our lab on monday was about trying to distinquish the difference between each and then identifying the different types of rocks in each category. We looked into foliation and how to tell if the rock has it or not. Also, we looked at the different types of sedimentary rocks and where they came from. Plus, we looked into a few more igneous rocks and saw what the cleavage and luster was to identify the name of the rock.
This weeks exam has a variety of material on it. Different types of foliation will be questioned, such as: shistosity, layers, flattened pebbles, and shearing. More topics include lineation: oriented minerals, stretched crystals, and shearing marks. We’ll look at the evolution of shale to slate to schist to gneiss due to different levels of high temperatures and high pressures. Other transformations due to high pressure and high temperatures are the shift from sandstone to quartzite, limestone to marble, and basalt or andesite to greenschist to gneiss. Also, the causes of metamorphism will be on the test including: burial, hot fluids (lava), subduction, change in stress, heating, and shearing. There are also four types of metamorphism. One is Hydrothermal metamorphism, which is the combination of low temperature and low pressure with igneous fluids (magma) and chemicals with water. Another is contact metamorphism, which is a combo between high temperatures with low pressure and is baked by escaping gas. A third is regional metamorphism, which is the type that most metamorphic rocks go through, which is a combo between high temperature and high pressure. The last type is blueschist metamorphism, which is a combo between low temperatures and high pressures; this is a rare type. The contact metamorphism usually occurs at magma chambers while the blueschist will usually occur at convergent boundaries.
During the week of class we covered a section on sedimentary environments that showed the three basic types: erosion, transport, and depostition. We learned that most sediment comes from mountatins and will erode because of rainfall or because of rivers. The steeper the river, the quicker the erosion. Sanddunes are deposited by wind or water, but mainly winds. The material that you would normally find in meandering rivers will be more fine as well as the material found in lakes, because of the stagnant or slowly moving waters. Beaches are formed from the oceans sedimentary dump from waves. The two ways of making sediment are physical weathering and chemical weathering, and hydrolysis, and oxidation. Physical weathering is fracturing, frost and mineral wedging, roots, and other biological activity. Chemical weathering involves dissolution. Finally, hydrolysis is oxidation, which means that oxygen will accept other electrons. Also, we learned that there are three basic clast sizes that make up boulders, cobbles, and pebbles, which are sand, silt, and clay. Clay being the finest of the three.