Geology Test: Igneous Rocks

Very early in Earth's history, it was so hot that the surface was entirely molten

True

A volcano emits ash, which falls from the sky, settles in layers, and is eventually cemented. The resultant rock is termed

Tuff

Which type of magma has the greatest iron and magnetic content?

Ultramafic

Important volatiles in magmas include

Water and carbon dioxide

A dike is

a tabular intrusion that cuts across preexisting layers

A sill is

a tabular intrusion that lies parallel to surrounding layers of sedimentary rock

If a body of magma becomes more felsic, its viscosity will

increase

If a body of magma cools, its viscosity will

increase

Typically, as magma ascends through the crust, its viscosity is expected to

increase

Coarse-grained diorite is most similar in mineral composition to fine-grained

Andesite

Most commonly, felsic igneous rocks

Are lighter in color than mafic rocks

Radioactive isotopes, differentiation of the Earth's iron core, gravity driven compression, and meteoric bombardment all caused early Earth to

Be much hotter than at present

All other factors being equal, intrusive rocks that form deep within Earth ______________ than intrusive rocks that cool near the surface

Cool more slowly

The formation of magma within Earth is not caused by which of the following Processes

Decompression, addition of volatiles, and transfer of heat from adjacent magma or very hot rocks (all of the above)

If the volatile content of magma is increased, its viscosity will

Decrease

All minerals within igneous rocks have a melting temperature of 750C

False

When rock is melted within Earth, typically the entire volume of rock is transformed from solid state to a liquid.

False

Which type of magma has the greatest silica content?

Felsic

Which type of magma is produced at the coolest temperatures?

Felsic

The grain size of an igneous rock is determined primarily by

How rapidly it cooled during crystallization

When magma crystallizes, _____________ are formed.

Intrusive igneous rock

Obsidian

Is volcanic glass, possesses conchoidal fracture, and typically is felsic in composition (all of the above)

If a body of igneous (source) rock is subjected to partial melting, the magma that is produced is expected to be

More felsic than the source rock

If a body of magma is subjected to fractional crystallization, the rock that results is expected to be

More mafic than the magma

Bombs, ash, and cinders are all examples of

Pyroclastic Debris

Igneous rocks

are formed through the freezing of melt, can be produced at the surface of the Earth as well as deep below the surface, and are the most common type of rocks within Earth (all of the above)

Close-grained gabbro is most similar in mineral composition to fine-grained

basalt

As compared to aphanitic igneous rocks, phaneritic rocks are

coarser grained

Volatiles refer to substances that

have a tendency to evaporate and are stable as gases

Geologically, melts are equivalent to both

lavas and magmas

The difference between lava and magma is that

magma is found beneath the Earth's surface, whereas lava has reached the surface

When very hot rock rises rapidly to the surface, it

may melt due to a decrease in pressure

The distinction between a pluton and a batholith is

numerous plutons make up batholith

A blob-like igneous rock body that has cooled beneath the surface of the Earth is

pluton

An igneous rock with a mixed texture of coarse grains (phenocrysts) surrounded by fine crystals (groundmass) is termed

porphyritic

Pegmatites, which occur in dikes, are unusual among shallow intrusive rocks in that they

possess exceptionally coarse grains

Coarse-grained granite is most similar in mineral composition to fine-grained

rhyolite

Recently formed magmas at depth have a tendency to

rise upward toward the surface

Pieces of country rock absorbed by an intrusive body and that do not melt form

xenoliths