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GLG 101 Week 4 Assignment
Axia College Material
Appendix H
Week Four Lab Report: Volcanic Products
Answer the lab questions for this week and summarize the lab experience using this form.
Full Name
Date
Carefully read pages 69-86 in Geoscience Laboratory.
Complete this week’s lab by filling in your responses to the questions from Geoscience
Laboratory. Select answers are provided for you in red font to assist you with your lab work.
Although you are only required to respond to the questions in this worksheet, you are encouraged
to answer others from the text on your own.
Lab Questions
4.8.
A. What do you suppose was the shape (in horizontal plan view) of the magma body
that pushed up the layers of sedimentary rocks that now comprise Green Mountain—
circular, amoeboid (irregular), or linear (elongated)?
Answer: circular
B. Judging from sketches in Figure 4.5 of the Lab book, which type of plutonic igneous
rock body do you suppose is buried beneath the layers of sedimentary rocks at
Green Mountain?
Answer: Granite, Diorite, Gabbro, and Peridotite (plutonic rocks)
4.9.
Granite comprising Stone Mountain crystallized from magma tens of kilometers
within the Earth, but uplift and erosion has since laid this pluton bare. Assuming that
erosion has only slightly modified the original shape of the more durable granite body,
which of the igneous rock bodies in Figure 4.5 does Stone Mountain most closely
resemble?
Answer: Stock
4.10.
The lip of the crater has been breached by a lava flow, and a deep furrow marks its path.
In what map direction did that lava move, southeastward or northwestward? (Notice the
arrow along the left margin of the page indicating north.)
Answer: southeastward
4.11.
Judging from the sizes of the before-and-after craters atop Mount St. Helens (Figs. 4.8
and 4.9 of the Lab book), which volcanic event appears to have been the more explosive,
the last one before 1980, or that which occurred in 1980?
Answer: That which occurred in 1980
GLG 101 Week 4 Assignment
4.14.
Applying the rule—the most complete form crystallizes first, and the least complete form
crystallizes last—list the four minerals in Figure 4.11 of the Lab book (W, X, Y, and Z) in
the order in which they crystallized. (Caution: The stack of cards in Figure 4.10 is 3dimensional, with one card upon another; whereas minerals in the thin-section in Figure
4.11 have essentially no depth. View this thin section as 2-dimensional, with minerals
side-by-side.
Answer: X, Z, Y, W
4.15.
If the granite in Figure 4.11 were melted in the laboratory, what would be the order in
which W, X, Y, and Z would melt? Hint: Imagine a pat of butter and a lump of sugar in a
sauce pan. Add heat. Which melts first? Maintain the heat until both have melted, then
turn off the heat. Which solidifies (crystallizes) first?
Answer: W, Y, Z, X
4.22.
(Refer to Figure 4.16. of the Lab book) Reflecting on the preceding paragraph, in what
way would you expect the chemical composition of an igneous rock crystallizing at X to
differ from that crystallizing at Y?
Answer: Rock at X would be richer in iron, magnesium, and calcium. Rock at Y would be
richer in silicon anions, aluminum, potassium, and sodium.
4.23.
In what textural way would you expect igneous rock crystallizing at Y to differ from that
crystallizing at Z? Hint: Which rock crystallizes more quickly?
Answer: Z would crystallize quicker than Y would crystallize. Rock at Y would be coarse
Textured and rock at Z would be fine textured.
4.25.
Where would you most likely find obsidian (volcanic glass), at W or at Z? Hint: See
obsidian’s compositional position in Table 4.1 on page 81 of the Lab book.
Answer: At Z
Lab Summary
Address the following questions in a 100- to 200-word summary:




Summarize the general principles and purpose of the lab.
Explain how this lab helped you better understand the topics and concepts addressed this
week.
Describe what you found challenging about this lab.
Describe what you found interesting about this lab.
Write your summary here:
The general principles and purpose of this week's lab was to help me learn
how to identify volcanic rocks by color, texture, and name. The lab helped me to
understand the different types of rocks that are created through volcanic
eruptions and how the lava affects the rocks. It was most interesting learning
GLG 101 Week 4 Assignment
about how some volcanoes are still listed as active and people still reside near
them. When a volcano erupts the lava can travel miles in seconds, so it seems
like a very big risk to take to live near an active volcano. The most challenging
part about the lab was trying to thoroughly understand sedimentary rocks and the
different aspects of sedimentary rocks. This week's lab was very challenging but
also very informative.
GLG 101 Week 4 Assignment
Axia College Material
Appendix G
Igneous Rock Identification
Full Name
Date
Examine the images of the five rocks. Identify as many characteristics as possible and enter the
information in the table below. Based upon the observed characteristics, identify each specimen
in the last column of the table. You may want to refer to Table 4.1 of Geoscience Laboratory (p.
81). Submit the completed Appendix in the Individual forum.
Rock Specimen
1.
2.
3.
4.
GLG 101 Week 4 Assignment
5.
Rock Identification
1.
x
2.
x
3.
5.
x
x
x
x
x
x
x
x
Rock Name
Pyroclastic
Porphyritic
x
Vesicular
Fine
x
Glassy
Coarse
x
x
4.
Recognizable Features
Very Dark
x
Texture
Dark
Intermediate
Color
Light
Specimen
number
Light colored feldspar
‘floating’ in sea of black fine
textured matrix
Light and dark gray,
feldspars, black
gerromagnesian minerals
Black volcanic crystalline rick
Porphyritic
basalt
Pink feldspars; glassy
transparent quartz; black
ferromagnesian minerals
Red to black wispy fabrics;
dense glass; conchoidal
fracture; sharp edges
White to light gray in color;
frosty glass; microscopic
pores impart a light weight
Granite
Diorite
Basalt
Obsidian
Pumice