1 Answers to Chapter 5 End of Chapter Questions 1. Why are some minerals stable several kilometers underground but unstable at the earth’s surface? The answer is due to weathering. Many minerals are quite thermodynamically “happy” in the high pressures, and hot and relatively dry conditions within the earth. However, exposure to the relatively cold and damp climates on or near the earth surface breaks these minerals down by either chemical weathering (chemical reactions which decompose the mineral into new chemical compounds) or mechanical weathering (the physical disintegration or breaking up of the mineral into smaller pieces). 2. Describe what happens to each mineral within granite during the complete chemical weathering of granite in a humid climate. List the final products for each mineral. Our granite will be made up of quartz, potassium feldspar, a little bit of plagioclase feldspar, some muscovite, and a little bit of hornblende. • Quartz is stable and survives as quartz throughout the weathering process • Potassium feldspar and plagioclase feldspar are unstable and break down into clay minerals (see part D, Table 5.1). In the case of potassium feldspar, K
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