Natural glass, such as obsidian, forms when magma:a.
cools too rapidly for crystals to form.
b. cools rapidly and very tiny crystals form.
c. cools too slowly for crystals to form.
d. doesn't cool.
e. none of these.
Q. 2 -
Igneous rocks with a texture that is so fine-grained that the crystals are too small to see is:
a. aphanitic.
b. porphyritic.
c. glassy.
d. phaneritic.
e. pyroclastic
Q. 3 -
Igneous rocks with a two-stage intrusive-extrusive origin are recognized by a texture that is:
a. aphanitic.
b. porphyritic.
c. glassy.
d. phaneritic.
e. pyroclastic.
Q. 4 -
Large crystals found in a fine-grained groundmass can indicate:a.
origin from a magma with an early intrusive phase followed by an extrusive phase.
b. origin from a magma with an early extrusive phase followed by an intrusive phase.
c. a rock of mixed volcanic-plutonic origin.
d. origin from a magma with an early intrusive phase followed by an extrusive phase AND a
rock of mixed volcanic-plutonic origin.
e. origin from a magma with an early extrusive phase followed by an intrusive phase AND a
rock of mixed volcanic-plutonic origin.
Q. 5 -
Aphanitic, phaneritic, and porphyritic are textural terms that:a.
refer to fine-grained, course-grained, and mixed-grained crystal sizes, respectively.
b. refer to formation by slow cooling, fast cooling, and mixed cooling rates, respectively.
c. are indicative of volcanic, plutonic, and mixed plutonic-volcanic origins, respectively.
d. refer to fine-grained, course-grained, and mixed-grained crystal sizes, respectively, AND
are indicative of volcanic, plutonic, and mixed plutonic-volcanic origins, respectively.
e. all of these.
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