GEOL 101: Exam 2

Fill in the blanks using the choices below: ____ are minerals typically found in igneous rocks that have a high silica content, whereas ____ are minerals that are typically found in igneous rocks with a low silica content.

Plagioclase feldspar and quartz; pyroxene and olivine

Name the hardest and softest mineral on the Moh's scale.

Diamond (hardest) and talc (softest)

What do pumice and scoria have in common?

They both exhibit a vesicular texture.

Most igneous rocks never reach the surface. However, igneous rocks other than those formed in volcanoes are found exposed on many parts of Earth. How do you account for this phenomenon?

They formed at depth and have been exposed by uplift and erosion. Submit

Other than space, what two additional factors are significant for a crystal to attain habit?

Time and necessary elements

What minerals make up half of Earth's crust?

Feldspars

Once a source rock partially melts, what does it produce?

Felsic magma and mafic residue Submit

Which of the following textures describes an igneous rock with anomalously large crystals?

Pegmatitic Submit

Which of the following is a basic structural component of the most common mineral group?

a silicon-oxygen tetrahedron

In addition to viscosity, which of the following parameters has an influence on whether a volcanic eruption will be effusive or violent?

amount of gas in the magma

Pyroclastic debris from a volcanic eruption can include _____.

ash and cinders Submit

Which of the following igneous rocks contains no mineral crystals?

obsidian

The pipelike feature through which magma travels upward from an underground magma chamber is called a _______.

conduit

A _______ is formed on the volcano summit by explosive eruptions and is composed of accumulated volcanic debris.

crater

What is the term for a tabular igneous pluton that occurs in an orientation that is discordant with the bedding surfaces of adjacent sedimentary rocks?

dike

Most magma on Earth is produced at ___ plate boundaries.

divergent

When lava erupts at Earth's surface, what type of rock is produced?

extrusive

Working in the field, you see a thin, dark-colored igneous sill across the valley. Without seeing the sill up close, what texture would you expect it to possess?

fine-grained

Which of the following is considered a ferromagnesian silicate? CHOOSE ALL THAT APPLY. garnet potassium feldspar muscovite quartz biotite

garnet and biotite

Which of the choices below lists the four basic compositional groups of igneous rocks, ranging from the highest silica content to the lowest silica content?

granitic, andesitic, basaltic, ultramafic

Igneous rocks of felsic composition have __________ and __________ relative to mafic igneous rocks.

greater silica; lower melting temperature

The volcanoes in the Ring of Fire are generally described as

having violent eruptions, as most of these volcanoes are composite cones which eject andesitic lava.

The ratio of silicon to oxygen atoms in silicate minerals depends on:

how the atoms in silicon-oxygen tetrahedra are shared. Submit

Which of the following is a mineral? Granite, Plastic, Water, Ice, Charcoal

ice

Crystallization of molten rock will produce ________ rocks.

igneous

A phaneritic texture is characteristic of a(n) __________ igneous rock that cooled __________.

intrusive; below the surface submit

Which of the following are common tectonic settings associated with volcanic activity?

island arcs, mantle plumes, continental rifts, continental arcs

The external expression of a mineral's orderly internal arrangement of atoms is referred to as:

its crystal form

What kind of volcano is this?

shield volcano

What is the term for a tabular igneous pluton that occurs in an orientation that is concordant with the bedding surfaces of adjacent sedimentary rocks?

sill

The amount or quality of light that is reflected from a mineral surface is known as __________.

luster

A ________ __________ results when magma collects or ponds due to its density being higher than that of overlaying materials.

magma chamber

What lies underneath volcanic features at Earth's surface?

magma chambers and volcanic conduits

The property of cleavage reflects:

mechanical breakage along planes of weakness within the mineral.

Regardless of their size, most rocks are made up of __________.

minerals

A scientist creates diamonds using high-pressure laboratory experiments. These diamonds are not considered minerals because which of the following requirements has been violated?

minerals must occur naturally

Which of the following is a present-day example of a continental rift?

the East African rift valley

Crystal habit is the shape that a mineral develops by the repetition of __________.

the basic unit cell of a mineral

In silicate minerals, the type of cleavage or fracture is influenced by:

the bonding of the silicon-oxygen tetrahedra within the mineral. Submit

A mineral's streak is _________.

the color of the mineral in powdered form

At a subduction zone, melting is triggered by _____.

the introduction of water

As a result of partial melting, magma originates in __________.

the mantle and crust

In a subduction zone, water driven from subducted oceanic crust causes __________.

the melting temperature of mantle rocks to decrease

What is luster?

the quality of light reflected from a mineral's surface

In what type of igneous feature would you find rocks with a vesicular texture?

the surface of a lava flow

Hornblende has _____ cleavage planes at _____ angles.

two; non-90°

A _______ is an opening where volcanic materials erupt at the Earth's surface, and can form on the flanks of a larger volcano in the case of a _________ ________.

vent; parasitic cone

Which type of volcanic hazard can decrease global temperatures?

volcanic ash

What is a volcanic conduit called after the conduit has solidified and been exposed by erosion?

volcanic neck

What geologic process is related to caldera formation?

volcanism

Which of the following gases is most abundant in basaltic lavas? carbon dioxide water vapor sulfur dioxide argon nitrogen

water vapor

What are the two most abundant elements in Earth's crust?

Oxygen and silicon Submit

Contrast pahoehoe and aa lava flows.

Pahoehoe flows exhibit smooth surfaces, are hotter, and are more fluid than aa flows, which exhibit jagged surfaces with sharp edges.

What is a lahar?

a mudflow of volcanic debris saturated with water Submit

Which of the following often forms after continental rifting?

a new ocean basin

Quartz exhibits __________.

conchoidal fracture

What is the difference between a dike and a sill?

A dike intrudes across sedimentary layers, and a sill intrudes between sedimentary layers.

What is required to generate an igneous rock with a fine-grained texture?

A fine-grained texture is the product of rapid cooling and crystallization of lava. Submit

What is an accessory mineral?

A mineral that makes up a relatively small portion of the total rock composition

Which of the following statements correctly describes a parasitic cone?

A parasitic cone is a small cone on the side or base of a volcano that has formed during repeated flank eruptions. Submit

What causes the same mineral to occur in varieties that are different colors?

A small amount of impurities in the crystal structure.

How is this chain of volcanic islands forming?

A tectonic plate is moving over a mantle plume, which burns through the plate to create a chain of volcanoes.

How do the crystallization and settling of the earliest formed minerals affect the composition of the remaining magma?

After the earliest formed minerals have settled, the resulting magma will be more felsic than the original magma.

Which of the following are examples of modern-day island arcs?

Aleutian Islands, Mariana Islands

What is the rock name of an intermediate rock with two distinct grain sizes?

Andesite porphyry

What causes an elevated geothermal gradient in a divergent plate setting?

Decompression melting of the mantle Submit

How is basaltic magma transformed into felsic magma?

Basaltic magma partially melts the continental crust, which is more felsic in composition.

Why does partial melting result in a magma having a composition different from the rock from which it was derived?

Because different minerals melt at different temperatures, minerals that melt at lower temperatures will melt from the rock first, creating a magma formed from the minerals that melted first.

What causes a lack of cleavage in some minerals?

Bonds of equal strength in all directions Submit

How are island arc and continental arc magmas similar?

Both are formed near subduction zones. Submit

Please compare and contrast muscovite and biotite.

Both muscovite and biotite are micas that have cleavage in one direction and have a shiny luster. However, unlike clear muscovite, biotite is black because it contains iron and magnesium.

Most marine organisms produce the mineral substance ________, which will later become limestone.

CaCO3

What mineral is not scratched by a fingernail, but is scratched by a copper penny?

Calcite

Consider a melt that has cooled to a temperature such that olivine, pyroxene, amphibole, and calcium-rich plagioclase feldspar have crystallized. Which elements will be depleted in the melt?

Calcium(Ca), Iron(Fe), Magnesium(Mg)

How do calderas form?

Calderas form when the summit of a volcano collapses.

Which of the following best describes the term cleavage?

Cleavage is the splitting of minerals along natural planes of weakness. Submit

Which mineral property is the least useful for identifying minerals, and why?

Color is the least useful property for identification, as the same mineral type can be found in several different colors due to impurities in the mineral

How are continental rift magmas and continental arc magmas different?

Continental arc magmas are more viscous than continental rift magmas. Submit

Suppose you found a mineral crystal that looked like topaz. What two minerals could you use in a scratch test to help determine if the mineral is indeed topaz?

Corundum and quartz Submit

Why does Crater Lake have an island in it?

The volcano is still active, and a new volcanic peak has formed.

How do light-colored igneous rocks differ from dark-colored rocks?

Dark-colored igneous rocks have a higher iron and magnesium content than light-colored rocks.

What is the difference between extrusive igneous rocks and intrusive igneous rocks?

Extrusive igneous rocks cool and solidify on the Earth's surface, whereas intrusive igneous rocks cool and solidify beneath the Earth's surface. Submit

What discourages minerals from achieving habit?

Enclosed spaces

All minerals have cleavage.

False

You have found a mafic rock with a phaneritic texture. What is a potential rock name?

Gabbro Submit

Which of the following exhibits three sets of cleavage at 90° angles?

Galena

Why glass is not considered a mineral?

Glass has a disorderly atomic structure.

Which of the following best describes the difference between granite and rhyolite?

Granite is phaneritic and rhyolite is aphanitic.

What are the economic uses of three common nonsilicate minerals?

Halite is used for common salt, gypsum is used in plaster, and graphite is used as pencil lead.

Which of the following is an example of modern-day mantle plume volcanism?

Hawaiian Islands

Intrusive and extrusive igneous rocks are classified based on what criteria?

How quickly the molten rock cools and crystallizes, and where this occurs with respect to Earth's surface Submit

What is the basic foundation of Moh's hardness scale?

If a mineral scratches an object, then the mineral is harder than the object.

How are igneous rocks formed?

Igneous rocks are formed by the cooling and crystallization of molten rock.

__________ SiO4 4- tetrahedra join with __________ ions to produce the mineral olivine in the rock peridotite.

Independent; Mg2+ and Fe2+ Submit

Why does magma have a tendency to rise after its formation?

It is less dense than the surrounding rock. Submit

What is one way a glassy texture forms?

Lava cools rapidly.

Which statement describes the composition and viscosity of the lava associated with shield volcanoes?

Lava from shield volcanoes is mafic and has a low viscosity.

Since color is not a very useful way to identify a mineral, what other optical property or properties can be used?

Luster and streak

Which of the following is true about mafic igneous rocks?

Mafic igneous rocks are rich in Fe, Mg, and Ca.

Based on the diagram shown in the video, name two minerals that are unlikely to coexist in the same igneous rock.

Muscovite and pyroxene

Use your understanding of Bowen's reaction series and crystal settling to determine which of the following mineral associations should not be found in nature.

Olivine, potassium feldspar, quartz

Where is Crater Lake?

Oregon

Which of the following textures indicates two stages of cooling and crystallization?

Porphyritic

Consider a melt that has cooled to a temperature such that olivine, pyroxene, amphibole, and calcium-rich plagioclase feldspar have crystallized. Which elements will be enriched in the melt?

Potassium(K), Sodium(Na), Silicon(Si)

Based on what you learned in this video, what minerals make up rhyolite?

Quartz, K-feldspar, and plagioclase feldspars, with relatively fewer biotite and amphiboles

What region of the world has the greatest concentration of composite volcanoes?

Ring of Fire

Which statement correctly describes rock-forming minerals and economic minerals?

Rock-forming minerals consist of a few types of minerals that are abundant in Earth's crust, whereas economic minerals are less abundant and are used extensively in the manufacture of products.

The micas (biotite and muscovite) exhibit what type of silicate structure?

Sheet

Which of the following pairs of elements are the most abundant in the continental crust?

Silicon and oxygen

Which of the following best describes the term streak?

The color of a powdered form of a mineral produced by rubbing it across a hard surface.

In addition to rock deposits, what evidence do we have that the eruption that preceded the formation of Crater Lake was very large?

The eruption was so large that the magma chamber under Crater Lake partially emptied, causing the volcano to become unstable and collapse.

What is the geothermal gradient, and how does it relate to the melting curve of peridotite?

The geothermal gradient is the increase in temperature with depth under the Earth's surface. The melting curve of peridotite is consistently higher than the geothermal gradient. Submit

What does it mean if an igneous rock has an aphanitic texture?

The igneous rock exhibits mineral crystals too small to see with the naked eye.

What does an igneous rock with a pyroclastic texture tell a geologist?

The rock was likely formed by a violent volcanic eruption.

Which of the following best describes mineral habit?

The shape a mineral grows into, given sufficient space.

What is an accurate description of the silicon-oxygen tetrahedron?

The silicon-oxygen tetrahedron is a four-sided figure with a silicon atom in the middle bonded to four neighboring oxygen atoms.

How is magma generated along convergent plate boundaries?

The subducting slab drives water and carbon dioxide into the mantle, which reduces the temperature at which it melts, allowing mantle rock to melt and rise.

Which of the following describes a texture containing bubble-shaped cavities?

Vesicular

Why are volcanic rocks often exposed at Earth's surface as hills, ridges, and mountains surrounded by areas of lower elevation?

Volcanic rocks are often more resistant to erosion than surrounding rock.

How does decompression melting occur?

When hot, solid mantle rock ascends, it moves to areas of lower pressure. This reduction in pressure allows the hot material to melt into a less compressed liquid phase.

What is a mantle plume?

a circular column of magma that rises from deep within Earth

The mineral fluorite is an example of:

a halide mineral.

In which of the following lava types would you expect to see the development of pahoehoe?

basaltic

Which of the following types of lava will most likely lead to a volcanic eruption of an effusive nature? rhyolitic andesitic basaltic

basaltic

What is a magma chamber called after the conduit has solidified and been exposed by erosion?

batholith

What is the term used to describe a very large, widespread, and deep intrusive body of igneous rock?

batholith

Which of the following terms is best described as a massive pluton?

batholith

Minerals must be solid, have an orderly atomic structure, have a recognized chemical composition, be naturally occurring, and __________.

be generally inorganic in origin

Depletion of the upper part of a magma chamber during a volcanic eruption can result in gravitational collapse of the volcanic summit to form a ________.

caldera

When contrasting lava from composite volcanoes to lava from shield volcanoes,

composite volcanoes most often produce silica-rich lavas with high viscosities, whereas shield volcanoes produce basaltic lavas with low viscosities.

Ultramafic rocks contain __________ and are commonly found in __________.

olivine; mantle Submit

Where are continental volcanic arcs found?

on the overriding plate near a subduction zone

The silicon-oxygen tetrahedron contains:

one silicon atom and four oxygen atoms.

Use your understanding of Bowen's reaction series to determine which of the rocks below will crystallize the fastest. The chemical composition of the rocks is: gabbro, diorite, granite, peridodite

peridodite

Which of these minerals would be the first to crystallize in a body of magma?

pyroxene

According to Bowen's Reaction Series, __________ is one of the first minerals to melt, but last to crystallize.

quartz

In the field, you find an unidentified mineral that is clear, exhibits conchoidal fracture, and can scratch glass. This mineral is most likely:

quartz

Hardness describes a mineral's __________.

resistance to being scratched

In which of the following lava types would you expect to find the greatest percentage of gases?

rhyolitic

In which of the following types of lavas would you expect to find the greatest production of pyroclastic material?

rhyolitic

Which of the following types of magma has the highest viscosity? andesitic rhyolitic basaltic

rhyolitic