Name: __________________________________________________
Date: _________________
Igneous Rock Identification
Objective: To identify igneous rocks by observing their physical characteristics and using the
Characteristics of Igneous Rocks chart
Pre-Lab: Use the passage below and your notes from class to compare and contrast Intrusive
and Extrusive Igneous rocks in the Venn Diagram below.
Igneous rocks are rocks that form when lava or magma cools. Lava and magma are both molten minerals.
Lava is magma that has come out of the volcano on the Earth’s surface.
Rock that is formed when lava cools is called extrusive or volcanic. Lava on the exterior of the volcano is
exposed to the air or water (underwater volcanoes) and cools quickly. These rocks sometimes don’t even have
time to form crystals; this produces a glassy texture. Sometimes gas gets trapped in the rock, giving the rock an
appearance of being spongy, vesicular texture. Rock that is formed when magma cools is called intrusive or
plutonic. Magma is in the interior of the volcano. The rock surrounding the volcano is an excellent insulator,
making the magma cool very slowly. The mineral crystals can grow very large.
Geologists also classify igneous rocks based on the minerals in the rock. Light colored and less dense
rocks are called felsic. Denser darker colored rocks are called mafic.
Since the internal arrangement of atoms is the critical factor in determining the properties of minerals,
how the magma cools determines what type of mineral forms.
INTRUSIVE
E
EXTRUSIVE
E
Word bank
Course-grained
Fine-grained
Formed by solidification of molten rock
Cool quickly
Cool slowly
Volcanic
Plutonic
Igneous
Formed inside the Earth
Formed outside the Earth
Procedure: Use the Scheme for Igneous Rock Identification Chart in your ESRT, magnifying lens, and
metric ruler to identify the names of the igneous rocks by circling the appropriate responses below.
Rock # 1
1. What is the crystal texture? (circle one):
Glassy
Vesicular
2. The crystal size is:
<1mm
1mm-10mm
non-crystalline
3. Looking at questions 1 and 2 the rock is:
4. The rock is:
INTRUSIVE
light colored (pink to light grey)
5. Looking at question number 4, the rock is:
FELSIC
Non-Vesicular
10mm or larger
EXTRUSIVE
dark colored (grey to green)
MAFIC
6. Based on the answers above, the rock is ______________________________________________.
Rock # 2
1. What is the crystal texture? (circle one):
Glassy
Vesicular
2. The crystal size is:
<1mm
1mm-10mm
non-crystalline
3. Looking at questions 1 and 2 the rock is:
4. The rock is:
INTRUSIVE
light colored (pink to light grey)
5. Looking at question number 4, the rock is:
FELSIC
Non-Vesicular
10mm or larger
EXTRUSIVE
dark colored (grey to green)
MAFIC
6. Based on the answers above, the rock is ______________________________________________.
Rock # 3
1. What is the crystal texture? (circle one):
Glassy
Vesicular
2. The crystal size is:
<1mm
1mm-10mm
non-crystalline
3. Looking at questions 1 and 2 the rock is:
4. The rock is:
INTRUSIVE
light colored (pink to light grey)
5. Looking at question number 4, the rock is:
FELSIC
Non-Vesicular
10mm or larger
EXTRUSIVE
dark colored (grey to green)
MAFIC
6. Based on the answers above, the rock is ______________________________________________.
Rock # 4
1. What is the crystal texture? (circle one):
Glassy
Vesicular
2. The crystal size is:
<1mm
1mm-10mm
non-crystalline
3. Looking at questions 1 and 2 the rock is:
4. The rock is:
INTRUSIVE
light colored (pink to light grey)
5. Looking at question number 4, the rock is:
Non-Vesicular
10mm or larger
EXTRUSIVE
dark colored (grey to green)
FELSIC
MAFIC
6. Based on the answers above, the rock is ______________________________________________.
Observations: Use the Characteristics of Igneous Rocks chart to answer.
1. What are the differences between Pumice and Basalt?
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2. What are the differences between Pumice and Scoria?
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3. Describe the main differences between felsic and mafic rocks:
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4. Describe the main differences between intrusive and extrusive rocks:
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