Questions and Answers
What three characteristics do geologists use to identify a rock sample?
Color, texture, and mineral composition.
What are the three groups into which geologists classify rocks?
Igneous rock, sedimentary rock, and metamorphic rock.
What is a rock's texture?
The look and feel of the rock's surface.
What methods do geologists use to determine the mineral composition of a rock?
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What do the three major groups of rocks have in common? How are they different?
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What are the three major characteristics that geologists use to identify igneous rocks?
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What is the difference between extrusive and intrusive rocks? Give an example of each.
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Explain what causes an igneous rock to have a fine-grained or coarse-grained texture.
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Why are some igneous rocks dark and others light?
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How are basalt and granite different in their origin, texture, and mineral composition? How are they similar?
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Once sediment has been deposited, what processes change it into sedimentary rock?
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What are the three major kinds of sedimentary rocks?
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Describe two ways in which limestone can form.
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Compare and contrast shale and sandstone. Include what they are made of and how they form.
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Explain how coral reefs form.
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How does coral become limestone?
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Why are living coral animals only found in water that is less than 40 meters deep?
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Would you expect to find coral reefs growing in the ocean near the mouth of the Amazon? Explain your answer.
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Describe the process by which metamorphic rocks form.
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What characteristics are used to classify metamorphic rocks?
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Which properties of a rock may change as the rock becomes metamorphic?
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How does pressure change rock?
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Why are you less likely to find fossils in metamorphic rocks than in sedimentary rocks?
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What process gradually changes rocks from one form to another?
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How can plate movements move rocks through the rock cycle?
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What rock comes before quartzite in the rock cycle? What rock or rocks could come just after quartzite in the rock cycle?
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Begin with a grain of sand on a beach. Describe what happens as you follow the grain through the rock cycle until it returns to a beach as a grain of sand again.
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In your opinion, at what point does the rock cycle really begin? Give reasons to your answer.
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Study Notes
Rock Identification
- Geologists identify rock samples by observing color, texture, and mineral composition.
- Rock texture refers to the appearance and feel of a rock's surface, particularly its grains.
Rock Classification
- Rocks are classified into three major groups: igneous, sedimentary, and metamorphic.
- Igneous rocks form from the cooling of molten rock; sedimentary rocks arise from compaction and cementation of particles; metamorphic rocks emerge from existing rocks altered by heat and pressure.
Igneous Rocks
- Characteristics to identify igneous rocks include origin, texture, and mineral composition.
- Extrusive rocks, like basalt, form from lava on Earth's surface; intrusive rocks, like granite, form from magma cooling underground.
- Texture varies based on cooling rates: rapid cooling creates fine-grained textures, while slow cooling results in coarse-grained textures.
Basalt vs. Granite
- Basalt is fine-grained and lacks quartz, primarily composed of feldspar and dark minerals; granite is coarse-grained, includes quartz, feldspar, and mica, and forms the cores of mountain ranges.
Sedimentary Rocks
- Sedimentary rocks are categorized into clastic (formed from fragments), organic (from living organisms), and chemical (from mineral precipitation).
- Limestone forms from calcite, precipitating from shells; shale consists of compacted clay particles while sandstone derives from cemented sand and quartz particles.
Coral Reefs Formation
- Coral reefs grow as coral animals produce calcite skeletons; these accumulate over time, layering and forming robust structures that can extend significantly.
- Living coral thrives in waters less than 40 meters deep due to light requirements for symbiotic algae.
Metamorphic Rocks
- Formed by intense pressure and temperature altering the original rock structure, changing texture and mineral content.
- Foliated metamorphic rocks exhibit grain arrangement in parallel layers or bands.
Rock Cycle Dynamics
- The rock cycle represents continuous processes transforming rocks among igneous, sedimentary, and metamorphic types.
- Plate tectonics drive the cycle, facilitating rock melting, uplift, and erosion.
From Sand to Sandstone and Beyond
- Sand transitions from beaches to sandstone, then subducted into the mantle to become magma, which may cool to form granite, erode back into sand, and repeat the cycle.
Conclusion on Rock Cycle's Start
- The rock cycle begins with magma; volcanic processes influence the Earth's geology, leading to various rock formations and transitions through these processes.
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Description
Test your understanding of fundamental geology concepts, including rock characteristics, classifications, and textures. This quiz will help reinforce your knowledge of the three major types of rocks and what geologists look for when identifying rock samples.