Why was obsidian a much sought after rock which was traded far and wide by the Native Americans? (For example, obsidian from Yellowstone Park was traded as far east as Ohio.)
Answer to relevant QuestionsWhat coarse-grained (plutonic) rock consists of abundant calcic plagioclase plus olivine and pyroxene?What are the rounded structures shown in Fig. 3.10?How do geologists determine whether hot ash flows (glowing avalanches) were minor or major events?If volcanoes are dangerous, as illustrated when Mt. St. Helens erupted in May 1980, why are some volcanic regions such as Sumatra in the East Indies so densely populated?How are talus piles below cliffs, as in Fig. 4.4, related to weathering?
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