111-15 - GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111...

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GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111 Lecture Note Series Weathering Lecture Goals A) Mineral Stability B) Types of weathering (Physical, Chemical, Biological) C) Chemical weathering reactions Reference: Press et al., 2004, Chapter7; Grotzinger et al., 2007, Chapter 16, p 371-381 A) Mineral Stability Are you glad to be finally done with igneous rocks? All those textures, all those compositions, all those minerals? Well the good news is that you are now done with igneous rocks. The bad news is that you still need to know Bowen’s Reaction Series. In a very short period of time (2 lectures?) we will start talking about the next group of rocks (the sedimentary rocks). Before we get to them though, we have to discuss the origin of sediment . Sediment is a diverse group of materials that are initially unconsolidated (fragmented) and that can be converted to rock (sedimentary rock) under the right conditions. One of the ways that sediment is produced is through the break up ( weathering ) of other rocks. Since we left off with igneous rocks, we might as well use them as an example of how the weathering process works. Igneous rocks are composed of minerals that form from molten rock. Minerals that form at high temperature and/or high pressure do so because they are stable under those conditions. Olivine is very stable at 1800 ° C, but at temperatures significantly less than that, like that at the surface of the Earth, olivine is unstable. Add water in the form of rain fall, and the mineral becomes very reactive. Olivine-rich rocks such as dunite, peridotite or basalt porphyry do not survive long at the surface of the Earth. Bowen’s Reaction Series can also be considered a stability series. Those
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111-15 - GY 111 Lecture Notes D. Haywick (2008-09) 1 GY 111...

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