Geology Reference
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12. What are the similarities and differences among dikes,
sills, and laccoliths?
13. How does pegmatite form and why are its minerals
so big?
14. Explain or diagram how a volcanic neck forms.
15. Two phaneritic igneous rocks have the following
compositions: Specimen 1-5% biotite; 15% sodium-
rich plagioclase; 60% potassium feldspar; and 10%
quartz. Specimen 2-10% olivine; 55% pyroxene;
5% hornblende; and 30% calcium-rich plagioclase.
Use Figure 4.10 to classify these rocks. Which one
would be darkest and densest? Explain how you know.
16. How do assimilation and stoping contribute to the
emplacement of a batholith in the crust?
17. Explain what a porphyritic texture is and how one
might develop.
18. Use Bowen's reaction series to explain the sequence
in which minerals crystallize from mafi c magma.
19. What generalizations can you make about the size
of minerals in igneous rocks and whether they are
volcanic or plutonic? Are there exceptions to your
generalizations?
20. What three processes account for the origin of
magma?
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