Quiz 8 Igneous Rock

_____________ is an extrusive igneous rock, generally white to dark gray with abundant vesicles; its density is so low that it may float on water.

pumice

Igneous rocks composed of fragments of rock and ash that have been hurled through the air and welded together by heat during explosive volcanic eruptions have this texture:

pyroclastic

According to Bowen's reaction series, what is the product of olivine's reaction with the melt, as temperature decreases and minerals start to crystallize out of the magma?

pyroxene

What is the first mineral to melt when a rock is heated, assuming that all minerals of the choices below are present within this rock?

quartz

Which minerals are most characteristic of a granite?

quartz, potassium feldspar, plagioclase feldspar, muscovite, and biotite

When metamorphic rocks are heated to the point that they begin to melt, magma is formed, which cools and crystallizes to form this rock type:

igneous

Igneous rocks composed mostly (but not entirely) of dark-colored ferromagnesian minerals (rich in iron and magnesium) and some feldspar are called:

Mafic

In Bowen's Reaction Series, the Discontinuous Reaction Series has these minerals in order from highest temperature to lowest temperature:

olivine, pyroxene, amphibole, biotite

Which minerals are most characteristic of a mafic rock like basalt or gabbro?

olivine, pyroxene, amphibole, plagioclase feldspar

Igneous rocks with very large grains (generally greater than 2 cm, or 1 inch) have this texture:

pegmatitic

What is the name of the texture displayed by this sample? (Note that the scale is in centimeters.)

phaneritic

The textural term for the large pink crystals in this rock is (scale in centimeters):

phenocrysts

Volcanic rocks that display large crystals contained within a finer grained groundmass have this texture:

porphyritic

The pink mineral in this rock is (scale in centimeters):

potassium feldspar (orthoclase)

The three minerals at the bottom of Bowen's Reaction Series, in order, from highest to lowest temperature, are...

potassium feldspar, muscovite, quartz

Large crystals in an igneous rock indicate:

slow cooling

The following is a mafic rock:

Basalt

How do xenoliths form?

By being engulfed as un-melted blocks of surrounding rock within ascending magma

A sheet-like pluton that cuts across the structure of the country rock (the regional rock where it is intruded) is _______.

DIke

Molten rock is called lava if it solidifies and crystallizes at depth.

False

A concordant pluton that is tabular or sheetlike is called a:

Sill

Identify the texture seen here (scale in centimeters):

Vesicular

Felsic rocks are characterized by ________.

all of the above except a

Identify the texture seen here (scale in centimeters):

aphanitic

Igneous rocks with crystals too small to see without the aid of a hand lens (less than 1 mm) have this texture:

aphanitic

Molten rock is called magma if it is where?

beneath the surface of the Earth

The following is/are a/n intermediate rocks:

both 1 and 2

The visually estimated percentage of dark minerals in a rock is the:

color index

Igneous rocks that form by the cooling of lava on the Earth's surface are called:

extrusive

The cooling history of an aphanitic rock is:

fast

The rock shown here is most likely to be of this composition (scale in centimeters):

felsic

According to the Rock Cycle, what processes lead to the formation of an igneous rock from any other kind of rock?

melting, cooling and crystallization

Which minerals are most characteristic of peridotite?

mostly olivine with some pyroxene

The dominant mineral in this rock is (scale in centimeters):

olivine

Which mineral crystallizes at a higher temperature?

olivine

Which mineral would NOT be found in a granite?

olivine

Using the information on the texture and composition, the name of the rock shown here is most likely to be (scale in centimeters):

rhyolite

The rock in this photo ________. Note that the scale is in centimeters. (Image courtesy of USGS.)

shows to stages of crystallization, one at depth followed by one at shallow level.

The rock shown here is most likely to be of this composition (scale in centimeters):

ultramafic

Gas bubbles trapped in rock are called:

vesicles