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Geology Exam 1

Lava flows are typically finer grained than intrusive igneous rocks. Why?

C. the extrusive magma cools quickly so the mineral grains do not have time to grow

The sizes, shapes, and arrangements of mineral grains in an igneous rock are known as ________.

D. texture

A ________ is an open cavity in a volcanic rock that was filled by a gas bubble when the lava was still mainly liquid.

A. vesicle

Which of the following igneous rocks exhibit aphanitic (fine-grained) texture?

B. andesite, rhyolite

Visible quartz and potassium feldspar grains are the main constituents in a ________.

A. granite

________ is a volcanic rock that is extremely vesicular and glassy.

B. Pumice

________ is composed mainly of ferromagnesian minerals.

D. Peridotite

Which of the following minerals crystallize early in Bowen's reaction series?

C. olivine

________ is the dominant feldspar in basalt.

A. Plagioclase

________ is characterized by very coarse mineral grains?

A. Pegmatite

________ has the same mineral composition as andesite.

A. Diorite

A(n) ________ texture would be most unlikely to occur in an extrusive igneous rock.

B. phaneritic

________ is named for a prominent, volcanic mountain range in western South America.

D. Andesite

Which of the following igneous rocks has the lowest silica (SiO2) content?

A. peridotite

The last minerals to crystallize on Bowen's Reaction Series are those found in igneous rocks with a ________ composition.

A. felsic

Change in the composition of magma caused by melting surrounding host rock is known as ________.

B. assimilation

Most lava crystallizes to form igneous rocks with phaneritic (coarse-grained) textures.


Basalt is the aphanitic or fine-grained equivalent of gabbro.


Plutonic rocks are intrusive and generally consist of mineral grains coarse enough to be readily visible in a hand sample.




Atoms of the same element, zinc for example, have the same number of ________.

A. protons in the nucleus

What mineral is the hardest known substance in nature?

C. diamond

Which mineral is composed of silicon dioxide (Si02)?

B. quartz

Which of the following minerals is a silicate?

C. muscovite

A cubic centimeter of quartz, olivine, and gold weigh 2.5, 3.0, and 19.8 grams respectively. This indicates that ________.

A. gold has a higher density and specific gravity than quartz and olivine

Which of the following minerals is in the mineral group known as mica?

A. muscovite

Which one of the following mineral groups exhibits a sheet-like silicate structure?

B. clays

The ion at the center of a silicate tetrahedron is surrounded by ________.

B. 4 oxygen ions

All silicate minerals contain which two elements?

B. silicon, oxygen

What element is the most abundant in the Earth's crust by weight?

C. oxygen

The strong tendency of certain minerals to break along smooth, parallel planes is known as ________.

B. cleavage

Which one of the following is not true for minerals?

D. they can be a liquid, solid, or glass

Which group of minerals are the most abundant in the Earth's crust?

C. silicates

Which of the following will react readily with acids such as hydrochloric?

C. calcite

Which of the following describes the light reflecting and transmission characteristics of a mineral?

B. luster

Hornblende and the other amphiboles have what type of silicate structure?

C. double chains

Calcite and dolomite are both carbonate minerals.


Graphite and diamond have the same chemical compositions, but different crystalline structures.


The micas, biotite and muscovite, both exhibit one direction of cleavage.


The terms "rock" and "mineral" have the same meaning.


________ magma is erupted at oceanic spreading centers (mid-ocean ridges).

B. Basaltic

The majority of the Earth's subduction zones are found in and around the ________ Ocean basin.

C. Pacific

Which of the following volcanoes are associated with hot spots?

D. the volcanoes of Hawaii and geysers in Yellowstone National Park

Which of the following best describes seamounts and islands of the deep ocean basins?

D. piles of basaltic lava flows built up from the ocean floor by multiple, summit and flank eruptions

________ are the most abundant gases emitted by volcanoes.

D. Water vapor and carbon dioxide

Which set of magma conditions produces the most explosive eruptions?

B. High viscosity and dissolved gas

________ destroyed the city of St. Pierre, Martinique in 1902.

A. A nuee ardente (pyroclastic flow)

Which kind of eruptive activity is most likely to be highly explosive?

A. eruptions of large composite cones (stratovolcanoes)

Kilauea and Mauna Loa are ________.

C. basaltic shield volcanoes

Mount St. Helens is ________.

A. an explosive stratovolcano

The average composition of rocks comprising a large composite cone or stratovolcano is similar to a (an) ________ magma.

D. andesitic

A ________ volcano is a very large, gently sloping mound composed mainly of basaltic lava flows.

A. shield

Why do magmas rise toward Earth's surface?

B. magmas are mainly liquid and contain dissolved fluids such as water; most are less dense than the adjacent solid rock

A ________ is an intrusive, igneous rock body that is tabular and concordant (parallel to adjacent sedimentary rocks).

C. sill

The viscosities of magmas increase with increasing silica content.


Magma generation at depth almost always involves partial melting, not complete melting of the source rock.


Most basaltic magmas are believed to form by partial melting of granite in the lower crust and upper mantle.


The addition of water can lower partial melting temperatures in silicate rocks.


Crater Lake in Oregon actually occupies a volcanic caldera.


Basaltic lavas are generally hotter and more viscous than andesitic lavas.


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