Geology 1 Questions for Chapter 4

1) Lava flows are typically finer grained than intrusive igneous rocks. Why? A) Intrusive magma is cooler because it is well insulated by the surrounding rock. B) Intrusive magma flows onto the Earth's surface and cools very slowly, allowing many small mineral grains to grow. C) The extrusive magma cools quickly so the mineral grains do not have time to grow. D) The extrusive magma, because it is deep below the surface, cools very slowly producing very small mineral grains.

2) Which magma is most likely to quench (congeal) to a natural glass? A) highly viscous; cools quickly B) highly viscous; cools slowly C) highly fluid; cools slowly D) highly fluid; cools quickly

3) The sizes, shapes, and arrangements of mineral grains in an igneous rock is known as ______. A) silica content B) texture C) mineral content D) Bowen's reaction series

Match the following rocks to their equivalent aphanitic or phaneritic igneous rocks.

A. aphanitic ! B. porphyritic ! C. phaneritic ! D. glassy

4) ______magma cools and consolidates without growth of mineral grains

5) ______mineral grains are of roughly equal size and coarse enough to be seen without a microscope or magnifying glass

6) ______rock has two or more distinctly different-sized populations of mineral grains

7) ______a magnifying glass or microscope is needed to see individual mineral grains

8) A ______is an open cavity in a volcanic rock that was filled by a gas bubble when the lava was still mainly liquid. A) porphyrocryst B) vesicle C) phenocryst D) xenocryst

9) Consider the Bowen's reaction series. Which mineral would you expect to see as a phenocryst in a porphyritic basalt? A) olivine B) quartz C) orthoclase D) sodium-rich plagioclase

Match the following rocks to their equivalent aphanitic or phaneritic igneous rocks.

A. andesite ! B. gabbro ! C. rhyolite

10) ______granite

11) ______basalt

11) ______basalt

12) ______diorite 13) Which of the following igneous rocks exhibit aphanitic texture? A) granite; gabbro B) andesite; rhyolite C) andesite; diorite D) rhyolite; gabbro

14) In a porphyritic volcanic rock, which mineral grains are the last to crystallize? A) phenocrysts The correct answer is 'D'. B) vesicles Phenocrysts are the first C) pegmatites minerals to crystallize. D) matrix or groundmass

15) Visible quartz and potassium feldspar grains are the main constituents in a ______. A) granite B) gabbro C) basalt D) rhyolite

16) Which of the following igneous rocks has a pyroclastic texture? A) rhyolitic tuff B) porphyritic basalt C) intrusive granite D) andesitic lava

17) ______is a volcanic rock that is extremely vesicular and glassy. A) Obsidian B) Pegmatite C) Tuff D) Pumice

18) ______is composed mainly of ferromagnesian minerals. A) Peridotite B) Rhyolite C) Andesite D) Granite

19) Which of the following minerals crystallize early in Bowen's reaction series? A) biotite B) quartz C) olivine D) muscovite

20) ______is the dominant feldspar in basalt. A) Plagioclase B) Microcline C) Orthoclase D) Pyroxene

21) Which of the following are used for studying rocks with a polarizing microscope? A) polished cubes B) broken chips C) thin sections D) grain karats 22) ______is characterized by very coarse mineral grains? A) Obsidian B) Pumice C) Pegmatite D) Granite

23) A (an) ______texture represents a single, long period of cooling and crystallization. A) glassy B) pyroclastic C) aphanitic D) phaneritic

24) ______has the same mineral composition as andesite. A) Basalt B) Granite C) Gabbro D) Diorite

25) What do pumice and obsidian have in common? A) basaltic composition B) glassy texture C) ultramafic composition D) phaneritic texture

26) Which of the following best describes an aphanitic texture? A) The rock is crystalline; mineral grains are too small to be visible without a magnifying lens or microscope. B) The mineral grains have glassy textures. C) The rock consists of broken, volcanic-rock and mineral fragments. D) The rock is crystalline; mineral grains are of distinctly different sizes.

27) A ______texture would be most unlikely to occur in an extrusive igneous rock. A) pyroclastic B) glassy Should be 'D' since extrusive rock generally C) aphanitic have fine grained or apanitic texture and are D) phaneritic therefore unllikely to have phaneritic texture.

28) ______is named for a prominent, volcanic mountain range in western South America. A) Basalt B) Andesite C) Pegmatite D) Peridotite

29) ______is the dominant lava erupted from volcanoes on Hawaii and Iceland. A) Rhyolite B) Andesite C) Peridotite D) Basalt

30) Which igneous rock or magma has the lowest silica (SiO2) content? A) granite B) basalt C) andesite D) peridotite 31) ______is thought to be common in the Earth's mantle but rare in the crust. A) Pumice B) Granite C) Pegmatite D) Peridotite

32) ______often contain gem-quality crystals of minerals such as beryl and tourmaline and high concentrations of relatively rare elements such as lithium, boron, and beryllium. A) Welded tuff sheets B) Basaltic lavas C) Granitic pegmatites D) Diorite plutons

33) The last minerals to crystallize on Bowen's Reaction Series result in igneous rocks with a ______composition. A) felsic B) intermediate C) mafic D) ultramafic

34) Changing the composition of magma by incorporating surrounding host rock is known as ______. A) magma mixing B) partial melting C) differentiation D) assimilation

35) All of the following are factors that affect the generation of magma except for ______. A) heat B) pressure C) crystal size D) volatiles