Chapter 5—Igneous Rocks
Name_________________
Section 5.1: What are Igneous Rocks?
p. 99
1. _______________ is an igneous rock made from magma.
2. An ____________ _________ is formed from the crystallization of magma.
3. Molten rock below Earth’s surface is [magma,
4. Molten rock on Earth’s surface is
[magma,
lava] (circle one)
lava]
5. Fine-grained igneous rocks that cool quickly on Earth’s surface are
[extrusive, intrusive] (circle one)
6. Coarse-grained igneous rocks that cool slowly beneath Earth’s surface are called
[extrusive, intrusive]
p. 100
7. [T, F] Magma is often a slushy mix of molten rock, gases, and mineral crystals.
8. [T, F] The elements found in magma are quite different from those found in
Earth’s crust.
9. [T, F ] The most abundant compound found in magma is silica.
10. Magmas are classified as ________________, __________________, and
__________________ based on the amount of SiO2 they contain.
11. Silica content affects _____________ ____________ and how quickly magma flows.
p. 101
12. [ T, F] In the laboratory, rocks must be heated from 8000oC to 12 000oC before they
melt.
13. [T, F] Heat in the upper mantle and lower crust may come, in part, from the
decay of radioactive elements.
14. Temperature generally [increases, decreases] with depth in Earth’s crust.
15. Pressure [increases, decreases] with depth in Earth’s crust.
16. [T, F] Rocks have the same melting point regardless of their depth.
17. As water content of magma increases, the melting point [increases, decreases].
p. 102
18. Different minerals have [the same, different] melting points.
19. [ T,
F]
All parts of a rock melt at the same time.
p. 103
20. When magma cools, it crystallizes in the [same order, reverse order] of
partial melting.
p. 105
21. (Olivine, feldspar, quartz) often occurs in veins because it crystallizes as
the last liquid portion of magma is squeezed into rock fractures.
p. 107 22. Rocks are classified by their _________________ ___________________.
Clues for identification can also come from grain size and texture.
23. The three main groups of igneous rocks are _______________, ______________,
and ______________________________.
24. Light-colored, high silica content rocks that contain quartz and feldspars are
_____________.
25. Dark-colored, low silica content rocks that are rich in iron and magnesium are
___________.
p. 108/109 26. Obsidian, which is glassy, has a _____________________ grain size.
It is (extrusive, intrusive).
27. Gabbro has crystals which may be larger than 1 cm. It is (extrusive, intrusive).
p. 110
28. A rock with two different sized crystals has a ________________ texture.
p. 111
29. Igneous rocks are strong because of their ___________________________.
30. Igneous rocks tend to be A. resistant to weathering
B. vulnerable to weathering
31. Which of the following is one of the most durable igneous rocks?
A. sandstone
B. granite
C. marble
p. 112
p. 113
32. What are pegmatites?
A. magmas of differing densities
33. What are kimberlites?
A. felsic rocks B. mafic rocks
B. veins of extremely large-grained minerals
C. ultramafic rocks
34. Diamonds can form only
A. under very low pressure B. under very high pressure C. above ground
35. Most of the world’s diamonds come from
A. Saudi Arabia B. United States C. South Africa