Laboratory Manual for Introductory Geology 4e

EXERCISE 5.3
Interpreting Igneous Cooling History from Grain Size (continued )
Name:
Course:
Section:
Date:
Rule 2 of magma cooling: Circle the correct choice in the following statement. Magma loses heat much (faster/slower)
when exposed to air or water than it does when surrounded by other rock because wall rock is a good insulator.
(c) Consider two cubes of steel measuring 1 m on a side. One is cut in half in each dimension to make eight smaller cubes.
1 m
0.5 m
1 m
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What is the surface area of the large cube? cm 2 Of the eight small cubes? cm 2
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lmagine that the large and small cubes are heated in a furnace to 500°C and removed. Which will cool faster, the
large cube or the smaller ones?
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Explain why this happens.
EXERCISE 5.4
Interpreting Porphyritic Textures
Name:
Course:
Section:
Date:
(a) Based on what you have deduced about magma cooling, how does a porphyritic texture form?
(b) Describe the cooling histories of the rocks shown in Figure 5.3 in as much detail as you can.
5.3a
(continued)