The Perfect Practice Test For Geology Exams
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- 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
- 4.________ magma cools and consolidates without growth of mineral grains
- A.
Aphanitic
- B.
Porphyritic
- C.
Phaneritic
- D.
Glassy
- 5.________ mineral grains are of roughly equal size and coarse enough to be seen without a microscope or magnifying glass
- A.
Aphanitic
- B.
Porphyritic
- C.
Phaneritic
- D.
Glassy
- 6.________ rock has two or more, distinctly different-sized populations of mineral grains
- A.
Aphanitic
- B.
Porphyritic
- C.
Phaneritic
- D.
Glassy
- 7.________ a magnifying glass or microscope is needed to see individual mineral grains
- A.
Aphanitic
- B.
Porphyritic
- C.
Phaneritic
- D.
Glassy
- 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
- 10.Which of the following igneous rocks exhibit aphanitic texture?
- A.
granite; gabbro
- B.
Andesite; rhyolite
- C.
Andesite; diorite
- D.
Rhyolite; gabbro
- 11.In a porphyritic volcanic rock, which mineral grains are the last to crystallize?
- A.
Phenocrysts
- B.
Vesicles
- C.
Pegmatites
- D.
Matrix or groundmass
- 12.Visible quartz and potassium feldspar grains are the main constituents in a ________.
- A.
Granite
- B.
Gabbro
- C.
Basalt
- D.
Rhyolite
- 13.Which of the following igneous rocks has a pyroclastic texture?
- A.
Rhyolitic tuff
- B.
Porphyritic basalt
- C.
Intrusive granite
- D.
Andesitic lava
- 14.________ is a volcanic rock that is extremely vesicular and glassy.
- A.
Obsidian
- B.
Pegmatite
- C.
Tuff
- D.
Pumice
- 15.________ is composed mainly of ferromagnesian minerals.
- A.
Peridotite
- B.
Rhyolite
- C.
Andesite
- D.
Granite
- 16.Which of the following minerals crystallize early in Bowen's reaction series?
- A.
Biotite
- B.
Quartz
- C.
Olivine
- D.
Muscovite
- 17.________ is the dominant feldspar in basalt.
- A.
Plagioclase
- B.
Microcline
- C.
Orthoclase
- D.
Pyroxene
- 18.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
- 19.________ is characterized by very coarse mineral grains?
- A.
Obsidian
- B.
Pumice
- C.
Pegmatite
- D.
Granite
- 20.In which of the following igneous rocks and environments would you expect to find unusually high concentrations of rare elements such as lithium, beryllium, and boron?
- A.
Basalt dike; fills a vertical fracture at shallow depth
- B.
Pumice lump; crystallized at depth in a mass of intrusive granite
- C.
Peridotite; crystallized at depth in the upper mantle
- D.
Pegmatite; crystallized from a water-rich, highly differentiated, residual magma
- 21.A (an) ________ texture represents a single, long period of cooling and crystallization.
- A.
Glassy
- B.
Pyroclastic
- C.
Aphanitic
- D.
Phaneritic
- 22.________ has the same mineral composition as andesite?
- A.
Basalt
- B.
Granite
- C.
Gabbro
- D.
Diorite
- 23.What do pumice and obsidian have in common?
- A.
Basaltic composition
- B.
Glassy texture
- C.
Ultramafic composition
- D.
Phaneritic texture
- 24.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.
- 25.A ________ texture would be most unlikely to occur in an extrusive igneous rock.
- A.
Pyroclastic
- B.
Glassy
- C.
Aphanitic
- D.
Phaneritic
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