Download ISL#11

ISL #___
Observing Igneous Rocks
Integrated Science 4
5/14
Name ____________________________ Per. _____
 Introduction
One line of evidence for the theory of plate tectonics is the pattern of volcanic activity around the
Earth’s surface. Volcanism tends to occur around the margins of tectonic plates. All volcanic activity
involves molten magma moving from the mantle into the crust and subsequently solidifying into rock as it
cools. However, not all volcanoes are the same. Differences include the chemistry of magma/lava, the type
of eruption and the type of igneous rocks that are formed.
Igneous rocks are classified according to their color, which indicates chemical composition, and their
crystal size, which indicates where they were formed. Intrusive rocks form beneath the Earths crust when
magma cools slowly. Extrusive igneous rocks form on the surface when lava cools very rapidly. Differences
in cooling rate determine the texture of igneous rocks. When magma cools slowly, it forms large crystals
and coarse-grained rocks. When magma cools rapidly, such as in water, it forms extremely small crystals
and glassy rocks. The color of igneous rocks indicates their mineral composition. Dark rocks usually contain
large amounts of iron and magnesium and are called mafic. Light rocks contain large amounts of silicon
and aluminum and are called felsic. Andesitic rocks are a mixture of light and dark colors, and are also
intermediate in terms of iron, magnesium, aluminum and silicon levels. In this laboratory, we will observe
color and crystal size in igneous rock types. We will use these observations to infer chemistry and depth of
formation. This will be the first in a series of three laboratories designed to examine the relationship
amongst igneous rocks, volcanism and plate tectonics.
 Procedures
1. Characterize: Complete the shaded sections of the Data Table.
 Record the characteristic Colors, Chemical Composition and relative Crystal Sizes of each rock type
in the appropriate row or column.
2. Categorize: Gather the actual rock samples.
 Observe each rock’s characteristics and place them into the appropriate unshaded box in the Data
Table. There will be one rock per box. After placing the rocks, have your teacher check your work.
3. Classify: Complete the unshaded sections of the Data Table.
 Considering trends in color, chemical composition and crystal size, put the name of each igneous
rock in the appropriate box. There will be one rock name per box: andesite, basalt, diorite, gabbro,
granite, obsidian, pumice, rhyolite, and scoria. Have your teacher check your work.
4. Analyze and Observe:
 With your naked eye, hand lenses and stereo microscopes, make thorough observations of each rock.
 Draw and color each rock in the appropriate unshaded box. Record additional observations about
color and crystal sizes as needed.
 Discussion
1. Describe the relationship between color, chemical composition and rock type in igneous rocks. Use
examples from this activity in your discussion.
2. Describe the relationship between crystal size and depth of formation in igneous rocks. Use examples
from this activity in your discussion.
 Further Study
3. What is the relationship between these observable differences and plate tectonics?
 Data Table: Classification of Common Igneous Rocks (Color, Chemistry, and Crystal Size Trends)
Felsic
ROCK TYPE:
Andesitic
Mafic
Colors:
Colors:
Colors:
Chemical Composition:
Chemical Composition:
Chemical Composition:
Name:__________________
Name:__________________
Name:__________________
Color(s) and sketch:
Color(s) and sketch:
Color(s) and sketch:
Crystal Size(s):
Crystal Size(s):
Crystal Size(s):
Name:__________________:
Name:__________________
Name:__________________
Color(s) and sketch:
Color(s) and sketch:
Color(s) and sketch:
Crystal Size(s):
Crystal Size(s):
Crystal Size(s):
Name:__________________
Name:__________________
Name:__________________
Color(s) and sketch:
Color(s) and sketch:
Color(s) and sketch:
DEPTH OF
FORMATION:
Relative crystal
size:
Extrusive
Relative crystal
size:
Intrusive
(Shallow
to
moderate
depth)
Relative crystal
size:
Intrusive
(Moderate
to great
depth)
Crystal Size(s):
Crystal Size(s):
Crystal Size(s):