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Geology 101 Name: Homework assignment 3 Due in class on by e-­‐mail Monday, October 19, 5 p.m. 1. So what is the difference between a mineral and a rock? Hint: Discuss the variance allowed in the percentage of elements in a mineral versus the percentage of minerals in a rock. 2. What origin story do all igneous rocks have in common? What variations in these stories is allowed (think “rates”)? 3. The process of lithification to make a sedimentary rock requires compaction and/or cementation to occur. Which of these is more important to turn a bunch of mud at the bottom of a lake into the sedimentary rock mudstone? Justify your choice. 4. Most of the copper ore found in the North Cascades Range is in a structure called a porphyry deposit. According to Wikipedia, “Porphyry copper deposits are copper ore bodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself.” Go to the last section of chapter 4 on Natural Resources, and determine which type of deposit listed in the text corresponds to these porphyry deposits. Explain how you made your choice. 5. Hey, the word “porphyry” shows up again in chapter 5 on page 135. Explain how the definition of porphyry given here (which describes a rock) is consistent with the use of the word in “porphyry deposit” in chapter 4.