Download met lab 1: introduction to metamorphic rocks

GEOLOGY 13.53: Igneous and Metamorphic Petrology
MET LAB 1: INTRODUCTION TO METAMORPHIC ROCKS
Learning Objectives:
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Students will be able to differentiate microtextures that characterize metamorphic
rocks from those of their sedimentary and igneous protoliths
•
Students will be able to describe general trends in microtexture development with
increasing grade in metamorphic rocks
Key Minerals: Biotite, Calcite, Chlorite, Dolomite, Garnet, Hornblende, Muscovite, Plagioclase,
Quartz
1. Thin-section 7345 is Berea sandstone (AKA Ohio Sandstone, a common building
stone) and thin-section 7376 is quartzite (Baraboo Formation, WI). Examine each of
these thin-sections and find areas where several quartz grains are in contact. Sketch
these grain-contact textures below.
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What are the most distinct textural differences between sandstone and quartzite?
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What textural terms describe grain-boundaries in the quartzite?
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How does the extinction of quartz compare in sandstone and quartzite? What does this
indicate about conditions associated with metamorphism?
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2. Thin-section 7359 is dolostone (Lockport Formation, NY) and thin-section 7372 is
Tate Marble (a common building stone from Georgia). Examine each of these.
Sketch examples of typical grain shapes and grain-contact textures below.
What are the most distinct textural differences between dolostone and marble?
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How does the distribution of grain size of carbonate minerals vary between the
dolostone and marble samples?
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How does the abundance of twins in carbonate minerals vary between the dolostone
and marble samples? How might conditions of metamorphism account for this
difference?
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3. Thin-section 7377 is slate (Martinsburg Formation, PA), thin-section 7378 is phyllite
(Orfordville Formation, VT), and thin-section 7499 is a schist from Vermont. Examine
each of these. Sketch examples of typical grain shapes and grain-contact textures
below.
What are the most distinct textural differences that develop with increasing metamorphic
grade from slate to schist?
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How do contacts between quartz crystals in the schist compare with those in quartzite,
or with carbonates in marble?
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In terms of chemical composition, how do minerals that are unique to high-grade rocks
(e.g., garnet) compare with minerals that are common in low-grade rocks (e.g., chlorite
and muscovite)?
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4. Thin-section W204 is gabbro, and thin-section Z3A is amphibolite. Examine each of
these. Sketch examples of typical grain shapes and grain-contact textures below.
What are the most distinct textural differences between gabbro and amphibolite?
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How do grain contacts between plagioclase in the amphibolite compare with those of
quartz in quartzite, and with carbonates in marble?
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How does the shape and orientation of plagioclase and hornblende crystals differ
between gabbro and amphibolite?
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