Question: How does a porphyritic rock as in Fig 3 6 b form
How does a porphyritic rock, as in Fig. 3.6(b), form?
Answer to relevant QuestionsName another factor, other than the rate of cooling, that can affect crystal size. Very coarse-grained intrusions of igneous rocks (pegmatites) are an example of this factor at work.What is the most obvious evidence that lava extruded under water?Name the coarse-grained (plutonic) rock consisting primarily of hornblende and sodic plagioclase.Note the similarities in the sketches of Mt. St. Helens (Fig. 3.11) and Crater Lake, Oregon (Fig. 3.12). Surmise how Crater Lake may have formed.What minerals commonly fill vesicles to form amygdules as in Fig. 3.10?
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