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METAMORPHIC ROCK LAB
• INTEGRATED SCIENE
• LAB 07
• Dr. Gregg Wilkerson and Larry Drennen
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LABORATORY SEVENMetamorphic Rocks, Processes, and ResourcesActivities 7.1, 7.4
BIG IDEAS: Metamorphic rock has changed to a new and different form while in the solid state––without melting. Metamorphic change occurs because of increased heat, pressure, differential stress, or hot
water. The mineralogy and texture of a metamorphic rock can be used to interpret its geologic history. This
provides us with a glimpse of structural and tectonic events in the past, and helps us understand current
processes occurring beyond our direct observation below Earth’s surface. If the rock has undergone less
intense metamorphism, we can often infer what the rock was like before metamorphism. Metamorphic
rocks are widely used in the arts and construction industries and are sources of industrial minerals and
energy.
THINK ABOUT IT (Key Questions):• What do metamorphic rocks look like? How can they be classified into groups? (Activity 7.1)
• What are the characteristics of metamorphic rocks, and how are they formed? (Activity 7.2)
• How are rock composition and texture used to classify, name, and interpret metamorphic rocks?
(Activities 7.3 & 7.4)
• What can metamorphic rocks tell us about Earth’s history and the environments in which the rocks
formed? (Activity 7.5)
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LABORATORY SEVENMetamorphic Rocks, Processes, and ResourcesActivities 7.1, 7.4
ACTIVITY 7.1: Metamorphic Rock Inquiry
No instructor-supplied materials are needed for this activity.
ACTIVITY 7.4: Hand Sample Analysis, Classification, and Origin
_____ metamorphic rock samples with identifying numbers/letters (one set per group of students)
_____ mineral analysis tools: pocket knife or steel masonry nails, wire nails, glass plates, streak plates, copper pipe or tubing, small magnets (one set per group of students)
_____ dropper bottle of dilute hydrochloric acid (1–3% HCl). If there is a sink in the room, it might be best to restrict the HCl testing to the sink where specimens can be washed and dried after being tested with acid.
INSTRUCTOR NOTES
Foliation. Metamorphic foliation develops as grains grow or plastically deform at high temperature in a differential stress field. New minerals grow at
equilibrium
with all of the relevant environmental variables (pressure, temperature, fluids, chemical/mineral composition, and so on). High-T crystal plasticity and
mineral phase equilibria are beyond this course level, so it takes thought and careful planning to provide students with useful concepts of foliation development that do not involve misconceptions.
Platy minerals (chlorite, micas) grow with their flat faces perpendicular to the greatest compressive stress. The flattening of a ball or cube of Silly
PuttyTM on a tabletop perpendicular to the force of gravity shows how a solid can slowly adjust its shape to a differential stress. This physical model
provides an analogy to the natural process of growing or plastically deforming mineral grains so that faces with a greater surface area are perpendicular to the greatest compressive stress; however, a putty is not a crystalline solid.
Other minerals adjust their size and shape to minimize the internal strain energy stored in their crystal lattices and grain boundaries. Higher flow
stresses result in smaller grain sizes due to dynamic recrystallization. The equant shape of soap bubbles is analogous to the least-energy shape for grain boundaries.
Foliation can also occur in ductile shear zones. The result is a rock called a mylonite, which forms because of localized shear deformation.
Be careful not to present physical models or suggest thought experiments that provide a misleading picture of how metamorphic foliation develops. It can be difficult to reverse a misconception after it takes hold in a novice geoscience student.
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Metamorphic RocksMetamorphism = Change
Changes in mineral composition and/or texture that can occur in any solid rock
• Changes due to increasing temperature and/or pressure and/or the presence of fluids.
• Temperatures high enough to promote chemical reactions but not high enough to cause melting
• Similar temperatures found deep in crust or near magma chambers
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ACTIVITY 7.1: Metamorphic Rock Inquiry
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ACTIVITY 7.1: Metamorphic Rock Inquiry
7.1A 1. This rock has alternating layers of dark minerals and light minerals. The layers seem somewhat irregular.
2.This rock is a fine-grained material that has been folded without breaking the layers.
3. This rock is composed of white calcite mineral grains that are about equal in size.
4. This is a layered rock with a shiny surface that might be due to tiny grains of muscovite, and some much larger garnets.
5. This is a very fine-grained rock that has been folded on a small scale so it looks wrinkled. It is probably layered, and its shiny surface might be due to grains of muscovite along the layers.
6. This layered rock seems to have abundant coarse muscovite grains. The layers seem irregular rather than flat.
7.1B Reflect & Discuss Answers will vary widely. The most obvious groups are probably “layered” and “not layered.”
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ACTIVITY 7.1: Metamorphic Rock Inquiry
7.1A1. This rock has alternating layers of dark minerals and light minerals. The layers seem somewhat irregular.
ACTIVITY 7.1: Metamorphic Rock Inquiry
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2.This rock is a fine-grained material that has been folded without breaking the layers.
ACTIVITY 7.1: Metamorphic Rock Inquiry
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3. This rock is composed of white calcite mineral grains that are about equal in size
ACTIVITY 7.1: Metamorphic Rock Inquiry
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4. This is a layered rock with a shiny surface that might be due to tiny grains of muscovite, and some much larger garnets.
ACTIVITY 7.1: Metamorphic Rock Inquiry
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5. This is a very fine-grained rock that has been folded on a small scale so it looks wrinkled. It is probably layered, and its shiny surface might be due to grains of muscovite along the layers.
ACTIVITY 7.1: Metamorphic Rock Inquiry
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6. This layered rock seems to have abundant coarse muscovite grains. The layers seem irregular
rather than flat.
ACTIVITY 7.1: Metamorphic Rock Inquiry
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ACTIVITY 7.1: Metamorphic Rock Inquiry
7.1B Reflect & Discuss Answers will vary widely. The most obvious groups are probably “layered” and “not layered.”
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Metamorphic Rocks, Processes, and ResourcesActivity 7.4
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Metamorphic Rocks, Processes, and ResourcesActivity 7.4
Marble
X
LimestoneCalcite
Anthracite Coal
X
Bituminous Coal
Coal
Schist Shale
XMica, Quartz,
Feldspar
Slate ShaleClayLayeredX
Gneiss
X
GraniteMica, Quartz, Feldspar
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Metamorphic Rocks, Processes, and ResourcesActivity 7.4
Meta -Conglomerate
Phyllite
Conglomerate
Various – Clastic sedimentary rock
X
X
Mica Slate
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Alternative Sample Set
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2
3
4
5
Anthracite Coal
Schist
Slate
Gneiss
X
X
Shale
Shale
Granite
Bituminous Coal
X
XMica, Quartz,
Feldspar
Mica, Quartz, Feldspar
Coal
Clay
Metamorphic Rocks, Processes, and ResourcesActivity 7.4
Layered
1
Quartzite
X
SandstoneQuartz sand
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6
Metamorphic Rocks, Processes, and ResourcesActivity 7.4
Marble
X
LimestoneCalcite
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Metamorphic Rocks, Processes, and ResourcesExamples
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© 2018 Pearson Education, Inc.
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