ANSWER KEY
d. melts.
Skills Worksheet
_____ 5. Three factors that affect
whether rock melts
include temperature,
pressure, and
a. the presence of fluids in
the rock.
b. the chemical
composition of the
rock.
c. the composition of the
fluid in the rock.
d. the chemical/fluid ratio
of the rock.
Directed
Reading - 6.2
Section: Igneous Rock
Use the terms from the list below to
complete the sentences that follow.
Each term may be used only once.
Crystalline
igneous rock
chemical composition
1. When magma cools and hardens,
_____ 6.Rock melts when
a. its temperature drops
below the melting point
of minerals in the rock.
b. its temperature rises
above the melting point
of minerals in the rock.
c. the air temperature
reaches 38ºC.
d. it breaks into
fragments.
it forms
______________________.
2. Most igneous rock can be
identified as
______________________becau
se the minerals in the rock
crystallize as igneous rock forms
_____ 7. Adding fluids to hot rock
generally
a. increases the melting
point of certain
minerals in the rock.
b. has no effect on the
melting point of certain
minerals in the rock.
c. decreases the melting
point of certain
minerals in the rock.
d. causes the rock to
crystallize.
from magma.
3. The ______________________of
minerals in the rock and its
texture determine the identity of
the igneous rock.
THE FORMATION OF MAGMA
In the space provided, write the letter
of the answer choice that best
completes each statement or best
answers each question.
_____ 4. Magma forms when rock
a. cools.
b. solidifies.
c. weathers.
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Rocks
ANSWER KEY
Directed Reading continued
minerals from the cooling
magma is called
a. partial cooling.
b. total freezing.
c. crystallization.
d. fractional
crystallization.
_____ 8. The first minerals to melt
have the
a. highest melting point.
b. lowest melting point.
c. darkest color.
d. lightest color.
_____ 13. Crystals that form during
fractional crystallization
a. settle in the middle of
the magma chamber.
b. settle at the bottom or
stick to the walls and
ceiling of the magma
chamber.
c. leave the magma
chamber.
d. dissolve in the magma
chamber.
_____ 9. The process by which
different minerals in rock
melt at different temperatures is called
a. meltdown.
b. partial melting.
c. total melting.
d. decomposition.
_____ 10. How does the cooling
process of magma
compare with the melting
process?
a. The cooling process is
the same as the process
of partial melting.
b. The cooling process is
the reverse of the
process of partial
melting.
c. The cooling process is
faster than the process
of partial melting.
d. The cooling process is
slower than the process
of partial melting.
_____ 11. As temperature drops, the
first minerals to crystallize
from magma have
a. the lowest freezing
point.
b. the highest freezing
point.
c. no freezing point.
d. the same freezing
points.
_____ 12. The crystallization and
removal of different
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Rocks
ANSWER KEY
Directed Reading continued
____________________________________________
_____ 14. In some crystals, why is
the chemical composition
of the inner part different
from that of the outer
part?
a. The crystallization took
place very quickly.
b. The crystallization
happened over a long
period.
c. The temperature of the
magma changed during
crystallization.
d. The composition of the
magma changed while
the crystal was
growing.
____________________________________________
23. What determines the texture of
igneous rock?
____________________________________________
24. What determines the size of
crystals in igneous rock?
____________________________________________
25. Large mineral crystals are
commonly found
in______________________.
TEXTURES OF IGNEOUS ROCKS
In the space provided, write the letter
of the description that best matches
the term or phrase.
_____ 15. intrusive igneous
rock
_____ 16. extrusive igneous
rock
_____ 17. coarse-grained
texture
_____ 18. fine-grained texture
_____ 19. porphyritic texture
_____ 20. glassy texture
_____ 21. vesicular texture
a. the texture of quickly cooled magma that
has a mixture of large and small crystals
b. the texture of quickly cooled magma that
contains dissolved gasses that become
trapped as bubbles
c. the texture of igneous rock that is
composed of small crystals
d. rock formed from the cooling and
solidification of lava at Earth’s surface
e. the texture of quickly cooled magma that
contains a small percentage of dissolved
gasses
f. rock formed from the cooling and solidification of magma beneath Earth’s surface
g. the texture of igneous rock that is
composed of large mineral grains
22. How do intrusive and extrusive
igneous rocks differ from each
other?
_______________________________________________________________
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Rocks
ANSWER KEY
Directed Reading continued
____________________________________________
26. An example of igneous rock with
____________________________________________
a coarse-grained texture is
____________________________________________
34. Name four examples of felsic
rock.
______________________.
27. Two examples of igneous rock
____________________________________________
with a fine-grained texture
____________________________________________
are______________________
____________________________________________
and ______________________
____________________________________________
28. A rock that has a glassy texture is
called.______________________
. ______________________.
29. Holes in a rock that result from
rapid cooling are called
______________________.
30. An example of igneous rock that
has a vesicular texture is
______________________.
COMPOSITION OF IGNEOUS
ROCKS
31. What determines the mineral
composition of an igneous rock?
_______________________________________________________________
_______________________________________________________________
32. Define felsic.
_______________________________________________________________
_______________________________________________________________
33. List five mineral components of
felsic rock.
_______________________________________________________________
_______________________________________________________________
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Rocks
ANSWER KEY
Directed Reading continued
____________________________________________
35. Define mafic.
____________________________________________
_______________________________________________________________
____________________________________________
_______________________________________________________________
_______________________________________________________________
36. List the main mineral components
of mafic rock.
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
37. What two components are
responsible for the dark color of
mafic rock?
_______________________________________________________________
_______________________________________________________________
38. Name two examples of mafic
rock.
_______________________________________________________________
_______________________________________________________________
39. What four minerals make up
rocks in the intermediate family?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
40. How does the silica content of an
intermediate rock compare with
that of a felsic or mafic rock?
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
41. Name two rocks from the
intermediate family.
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Rocks
ANSWER KEY
Directed Reading continued
INTRUSIVE IGNEOUS ROCK
STRUCTURES
In the space provided, write the letter
of the description that best matches
the term or phrase.
_____ 42. intrusion
_____ 43. batholith
_____ 44. stock
_____ 45. laccolith
_____ 46. sill
_____ 47. dike
a. the largest of all intrusions; spreads at least
100 km2 when exposed on Earth’s surface
b. a dome that forms when magma flows between
rock layers and spreads
c. an igneous rock mass that forms underground
d. a mass that forms when magma flows between
rock layers and hardens; lies parallel to the
rock layers that surround it
e. an intrusion similar to a batholith; covers less
than 100 km2 of Earth’s surface
f. a mass that forms when magma flows and
hardens across layers of rock rather than
parallel to them
EXTRUSIVE IGNEOUS ROCK
STRUCTURES
In the space provided, write the letter
of the description that best matches
the term or phrase.
_____ 50. extrusion
_____ 51. volcano
_____ 52. volcanic neck
_____ 53. lava flow
_____ 54. lava plateau
_____ 55. tuff
a. an extrusion that takes the form of a flat mass
of rock
b. volcanic ash deposits that form during an
eruption
c. an igneous rock mass that forms on Earth’s
surface
d. a series of lava flows that cover a vast area with
thick rock
e. the solidified central vent that remains after the
soft parts of a volcano are eroded by wind and
water
f. a vent through which magma, gases, or volcanic
ash is expelled
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