READING QUESTIONS: Rocks
PSCI 131
Fall 2015
NAME________________________
DUE: Monday, December 7th
60 pts
Igneous Rocks: “Formed by Fire” (p. 34-43)
1. What is magma? __________________________________________________________________
2. Extrusive igneous rocks form at the Earth’s ________________, and intrusive igneous rocks form deep
____________________. (2 pts)
3. Fill in the blanks: The rate of cooling strongly influences _____________________. If magma cools
very _____________, ions can migrate over great distances. Consequently, _________ cooling results
in the formation of fewer, _________________ crystals. On the other hand, if cooling occurs
________________, the ions lose their motion and quickly combine. This results in a large number of
________ crystals all competing for the available ions. Therefore, rapid cooling results in the formation
of a solid mass of _____________ intergrown crystals. (4 pts)
4. To what mineral group do almost all minerals found in igneous rocks belong? ____________________
5. Explain how porphyritic texture forms. (4 pts) _____________________________________________
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6. List the four igneous compositional groups in order of decreasing silica content, and in order of
increasingly darker color. (4 pts)
Most silica
a. ______________________________
Lightest color
a. _______________________________
b. ______________________________
b. ______________________________
c. ______________________________
c. ______________________________
d. ______________________________
d. ______________________________
Least silica
Darkest color
7. Match each of the following igneous textural terms to the correct definition: (3 pts)
a. Coarse-grained
Composed of unordered atoms
_____
b. Fine-grained
Crystals large enough to be seen without a microscope
_____
c. Vesicular
Contains voids left by escaping magma gases
_____
d. Glassy
Composed of two distinctly different crystal sizes
_____
e. Porphyritic
Fragmental; composed of ash and larger rock fragments
_____
f. Pyroclastic
Crystals too small to see without a microscope
_____
8. Fill in this igneous classification chart with the correct rock names. Refer to Figure 7 on page 39. (4 pts)
Granitic
Andesitic
Basaltic
Ultramafic
Coarse-grained
Fine-grained
9. According to Bowen’s Reaction Series (p. 42), which of the following is the correct order of mineral
crystallization from a cooling magma?
a. Pyroxene, then amphibole, then olivine, then biotite
b. Olivine, then pyroxene, then amphibole, then biotite
c. Olivine, then amphibole, then biotite, then pyroxene
d. Biotite, then amphibole, then pyroxene, then olivine
10. During crystal settling, earlier formed minerals are more ___________ than the liquid portion and
________ towards the bottom of the magma chamber. When the remaining molten material solidifies, it
will form a rock with a ___________________________ much ________________ from the parent
magma. (2 pts)
Sedimentary Rocks: Compacted and Cemented Sediment (p. 43-49)
11. About _____% of rock exposed at Earth’s surface is sedimentary rock.
12. What two minerals are most abundant in detrital sedimentary rocks? ____________________________
(2 pts)
13. Match each detrital sedimentary rock to its description. (3 pts)
a. Conglomerate
Sandstone with abundant feldspar grains
______
b. Breccia
Very fine-grained sediment
______
c. Sandstone
Medium-grained sediment, little or no feldspar grains
______
d. Arkose
Fine-grained sediment
______
e. Siltstone
Coarse-grained, angular sediment
______
f. Shale
Coarse-grained, rounded sediment
______
14. For each chemical sedimentary rock listed, indicate whether it is biochemical or inorganic. (3 pts)
a. Coquina
_______________________
b. Chalk
_______________________
c. Rock salt
_______________________
d. Crystalline limestone
_______________________
e. Travertine
_______________________
f. Fossiliferous limestone
_______________________
15. Fill in the blanks: ____________________ refers to the processes by which sediments are transformed
into sedimentary rocks. One of the most common processes is _______________________. As
sediments accumulate over time, the weight of the overlying sediments __________________ the
deeper sediments. As the grains are pressed closer and closer, _______________________ is greatly
reduced. Compaction is most effective in converting ____________________________ into
sedimentary rocks. (3 pts)
16. Fill in the blanks: Because sand and coarse sediments are not easily compressed, they are generally
transformed into sedimentary rock by the process of ______________________. The cementing
materials are carried in a ____________________________ that percolates through the pore spaces
between particles. The cement _________________________ onto the sediment grains, _________ the
open spaces, and acts like a ___________ to join the particles together. (3 pts)
17. Give an example of one rock type that is lithified by compaction, and one that is lithified by cementation.
(2 pts)
a. Compaction: ____________________________
b. Cementation: ___________________________
18. If a geologist working in a barren desert encounters a layer of coal in an outcrop, and determines that the
layer is 200 million years old, what environment must have existed at that time in that location that is
very different from the modern desert environment?
_____________________________
Metamorphic Rocks: New Rock from Old (p. 50-54)
19. Metamorphism is a process that leads to changes in the _____________________, _________________,
and sometimes ____________________________________ of rocks. Most metamorphic changes occur
at the elevated ____________________ and ____________________ that exist in the zone beginning
_________________________ below Earth’s surface and extending into the _________________. (4
pts)
20. During metamorphism, rocks usually get hot enough to melt completely. TRUE or FALSE
21. How does contact metamorphism take place? (2 pts) _________________________________________
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22. List the four agents of metamorphism. (2 pts)
a. _________________________________
b. _________________________________
c. _________________________________
d. _________________________________
23. Which agent is the most important, and why? (3 pts) ________________________________________
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24. What is the difference between differential stress and confining pressure? (2 pts)
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25. Fill in the blanks: Foliation refers to any nearly ___________ arrangement of mineral grains or
structural features within a rock. In metamorphic environments, foliation is ultimately driven by
___________________________ that _________________ rock units, causing mineral grains in
preexisting rocks to develop __________________ alignments. (2 pts)
26. EXTRA CREDIT: Label each photo below with the type of foliation shown (rock cleavage,
compositional banding, or alignment of flat minerals – each will be used once). (3 pts)
_____________________________
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