Download Igneous Rock Questions

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Igneous Rock Questions
 Read “Exercises in Physical Geology” pages 24-37 and answer the following:
[1]
Define igneous rock.
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[2]
How does lava differ from magma?
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[3]
Igneous rocks are usually classified according to their _________________________ and
_________________________.
[4]
What is meant by the texture of igneous rock?
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[5]
How does the rate of cooling influence the crystallization process?
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[6]
The statements that follow relate to terms describing igneous rock textures. For each
statement, identify the appropriate term.
[7]
(a)
Openings produced by escaping gases.
(b)
Obsidian exhibits this texture.
(c)
A matrix of fine crystals surrounding phenocrysts.
(d)
Crystals are too small to be seen with the unaided eye.
(e)
A texture characterized by two distinctly different crystal sizes
(f)
Coarse grained, with crystals of roughly equal size.
What does a porphyritic texture indicate about igneous rock?
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[8]
How are granite and rhyolite different? In what way are they similar?
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[9]
A simple field method of identifying igneous rocks is to classify them according to
whether they are ____________________ or _____________________ coloured. If the
rock is light-coloured (white, gray, pink, red) it is composed largely of the silicaaluminum (silicic) group of minerals. The four most common minerals in this group are
_____________________, _____________________, _____________________ and
_____________________. The rock also will be relatively _____________________ in
weight. If the rock is dark-coloured (black, dark gray, dark green) it is composed largely
of the iron-magnesium-calcium (mafic) group of minerals. The four most common
minerals in this group are _____________________, _____________________,
_____________________ and _____________________. The rock also will be
relatively _____________________ in weight.
[10]
The above eight minerals are the main constituents of igneous rocks. The size of the
mineral grains (crystals) in the rock is known as _____________________. The
_____________________ of cooling of the magma determines the size of the mineral
grains. If the cooling of magma is slow, the chemical compounds within the magma had
sufficient time to develop into _____________________ and form a rock with a
_____________________ texture. Rocks with easily visible minerals were formed
_____________________ the earth’s surface. Rocks which cooled on or near the surface
cooled more rapidly, so their mineral grains are too small to be seen. Such rocks appear
very dense and have an_____________________ texture. If the magma cooled so
rapidly that no crystals developed at all, the rocks have a _____________________
texture. Igneous rocks which formed by the cooling and hardening of magma below the
surface are called _____________________ while those that formed on the surface are
called _____________________.