Geology 1 Questions for Chapter 4 1) Lava Flows Are Typically Finer

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.

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