Questions and Answers
What is a metamorphic rock?
A metamorphic rock is a rock whose original form and/or mineralogy has been changed, through pressure and/or temperature changes.
What are the two major types of texture in metamorphic rocks?
How can foliation be recognized?
Foliation can manifest as a visible alignment of minerals or a tendency for the rock to break along planes.
Describe progressive metamorphism in metamorphic rocks.
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Describe the low grade metamorphic rocks.
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Describe the medium to high grade metamorphic rocks.
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Describe the nonfoliated metamorphic rocks.
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Study Notes
Metamorphic Rocks Overview
- Metamorphic rocks originate from preexisting rocks, known as parent rocks or protoliths, altered by temperature and pressure changes below Earth's surface.
Types of Metamorphic Texture
- Foliated rocks exhibit a preferred alignment of platy minerals, whereas nonfoliated (granular) rocks lack this alignment, often indicating an absence of platy minerals.
Recognizing Foliation
- Foliation can appear as visible mineral alignment or microscopic alignment that leads rocks to break along specific planes due to the weakness created by the aligned minerals.
Progressive Metamorphism
- Foliated rocks are classified by metamorphic grade:
- Low-grade examples: Slate and phyllite, formed under low temperature and pressure.
- High-grade examples: Schist and gneiss, formed under high temperature and pressure.
Low-Grade Metamorphic Rocks
- Slate: Composed of clay minerals from shale; transformed into mica minerals that align and cause the rock to break along these planes.
- Phyllite: Contains micas larger than those in slate, imparting a sheen; also breaks parallel to aligned micas.
Medium to High-Grade Metamorphic Rocks
- Schist: Contains visible aligned micas; common minerals include biotite, muscovite, chlorite, and garnet; may feature porphyroblasts—large crystals embedded in the rock.
- Gneiss: Distinguished by coarse-grained minerals arranged in parallel, discontinuous light and dark bands, ranging from 1 to several centimeters thick.
Nonfoliated Metamorphic Rocks
- Composed of coarse-grained minerals that do not exhibit alignment.
- Marble: Derived from limestone, typically white to pink; identified by its inability to scratch glass.
- Quartzite: Originates from quartz sandstone, can also be white to pink; harder than marble, able to scratch glass.
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Description
This quiz covers key concepts related to metamorphic rocks, including their definitions and types of textures. Perfect for students studying geology, it provides a quick reference to essential terms and concepts. Test your knowledge and improve your understanding of this fascinating topic!
