Chapter 4: Igneous Rocks
 
 

1.	Which of the following igneous rocks crystallizes near the Earth's surface? A. basalt B. gabbro C. granite D. peridotite

 

2.	Which of the following rocks is a volcanic rock made up of lithified pyroclastic material? A. basalt B. granodiorite C. obsidian D. tuff

 

3.	Which of the following describes a rock with 10-millimeter-long plagioclase crystals "floating" in a fine-grained matrix of 0.5-millimeter long crystals? A. pluton B. porphyry C. tuff D. obsidian

 

4.	What is the approximate silica content of a granite? A. 30 percent B. 50 percent C. 70 percent D. 90 percent

 

5.	Andesite is an example of a(n) __________ igneous rock. A. felsic B. intermediate C. mafic D. ultramafic

 

6.	Which of the following best describes a basalt? A. fine-grained igneous rock rich in silica B. fine-grained igneous rock poor in silica C. coarse-grained igneous rock rich in silica D. coarse-grained igneous rock poor in silica

 

7.	Which of the following best describes the igneous rock depicted in the diagram above? A. basalt B. diorite C. granite D. rhyolite

 

8.	Which of the following best describes an andesite? A. a coarse-grained, intermediate igneous rock B. a fine-grained, intermediate igneous rock C. a coarse-grained, felsic igneous rock D. a fine-grained, felsic igneous rock

 

9.	Which of the following pairs of intrusive and extrusive rocks have the same chemical composition? A. granite and andesite B. diorite and basalt C. gabbro and basalt D. gabbro and rhyolite

 

10.	Which of the following properties increases in the direction of the arrows in the diagram above? A. melting temperature B. potassium content C. silica content D. viscosity

 

11.	Which of the following statements is true? A. Gabbro has a higher melting temperature than granite. B. Gabbro has a higher potassium content than granite. C. Gabbro has a higher silica content than granite. D. Gabbro has a higher viscosity than granite.

 

12.

Which of the following statements about felsic igneous rocks is true? A. Felsic rocks are richer in silica than mafic rocks. B. Felsic rocks crystallize at higher temperatures than mafic rocks. C. Felsic rocks tend to be darker-colored than mafic rocks. D. Felsic rocks tend to be finer-grained than mafic rocks.

 

13.	Which of the following lists is in the correct order of increasing amounts of silica? A. diorite ® granite ® gabbro  B. granite ® diorite ® gabbro  C. gabbro ® granite ® diorite  D. gabbro ® diorite ® granite

 

14.	Abundant felsic magmas occur in which of the following tectonic settings? A. continental volcanic arcs B. hot spots (mantle plumes) C. mid-ocean ridges D. oceanic volcanic arcs

 

15.	Which igneous rock is the most abundant igneous rock of the crust and underlies virtually all of the floors of the ocean? A. andesite B. basalt C. dacite D. granite

 

16.

What is the effect of water on melting? A. Water raises the melting temperature of a rock. B. Water lowers the melting temperature of a rock. C. Water raises or lowers the melting temperature of a rock depending on the composition of the rock. D. Water does not change the melting temperature of a rock.

 

17.	What type of magma forms at mid-ocean ridges? A. andesite B. basalt C. granite D. peridotite

 

18.	Which of the following minerals crystallizes from a magma at the highest temperature? A. biotite B. olivine C. orthoclase feldspar D. quartz

 

19.	Which of the following igneous bodies is a concordant intrusive rock? A. dike B. pluton C. sill D. stock

 

20.

How can a sill be distinguished from a lava flow? A. A sill is generally coarser grained than a lava flow. B. The rocks above and below a sill will show evidence of heating, but only the rocks below a lava flow will show evidence of heating. C. Sills generally do not have vesicles; lava flows generally do have vesicles. D. All of the above.

 

21.	Which of the following best describes the gray igneous rock depicted in the cross section above? A. dike B. lava flow C. pluton D. sill

 

22.

Compared to the mantle beneath a mid-ocean ridge, the mantle above a subduction zone __________. A. contains less water and melts at a lower temperature B. contains less water and melts at a higher temperature C. contains more water and melts at a lower temperature D. contains more water and melts at a higher temperature

 

23.	Which of the following is not a volcanic arc that overlies a subduction zone? A. Aleutian Islands (Alaska) B. Hawaiian Islands C. Cascade Range (northern California, Oregon, and Washington) D. Japanese Islands

 

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