GEOLOGY 111 ONLINE–GEOLOGY
IGNEOUS ROCK IDENTIFICATION ASSIGNMENT #1C (40 pts)
Igneous Rocks
Igneous rocks are made up of intergrown mineral crystals formed by the cooling and
solidification of magma or lava. Igneous rocks are classified on the basis of their mineral
composition (felsic, intermediate, mafic or ultramafic) and texture (aphanitic, phaneritic,
porphyritic, glassy, vesicular or pyroclastic). The composition gives information about the type
of magma from which it formed. Generally, more felsic minerals are lighter in color, including
pink, while more mafic minerals are darker in color, including green. The texture provides
insight into the cooling history of the magma. Coarse grained rocks are ones that individual
minerals are visible to the naked eye, cooling very slowly beneath the Earth’s surface. Fine
grained rocks contain minerals too small to be seen with the naked eye, cooling at the4 Earth’s
surface very quickly. Use the information from igneous rock classification chart below to
identify the ten unknown igneous rock names (granite, basalt, gabbro, diorite, rhyolite, tuff,
scoria, andesite porphyry, peridotite and obsidian). Use sections 5.1, 5.2 and 5.3 in the
textbook for assistance.
1
IGNEOUS ROCK IDENTIFICATION CHART
Sample
Number
Texture (Aphanitic,
Phaneritic, Porphyritic,
Glassy, Vesicular or
Pyroclastic)
Mineral Composition
(Felsic, Intermediate,
Mafic or Ultramafic)
Cooling History
(Fast, Slow,
Two-Stage)
Rock
Name
#1
#2
#3
#4
#5
#6
#7
#8
#9
#10
For each sample, answer the following questions by filling in the chart above.
What is the texture?
What is the mineral composition?
What is the name of the rock?
What is the cooling history of this mineral?
After completing the igneous identification rock chart above, you will then take a 20-question
multiple choice quiz on the assignment in Blackboard. Be sure to complete the chart before
taking the quiz.
2
Sample #1
3
Sample #2
Close-Up Look
4
Sample #3
Close-Up Look
5
Sample #4
6
Sample #5
7
Sample #6
8
Sample #7
9
Sample #8
10
Sample #9
Hint: Falls Apart Easily
11
Sample #10
Close-Up Look
12
13