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