Questions and Answers
Which of the following is true based on your observation of intrusive igneous rocks on Earth's surface?
Match the following intrusions with their descriptions:
Sill = Injected parallel to sedimentary layers, nearly horizontal orientation Dike = Cuts across sedimentary layers, nearly vertical orientation
Rank the following events in order from oldest to youngest in age.
- Magma is injected far below Earth's surface cutting through sedimentary rocks; 2. Magma crystallizes and a Dike is formed; 3. Sedimentary country rocks are eroded away; 4. Humans build a tunnel and road through the resistant igneous rocks.
Based on observations from the two previous photos, which sketch is the most accurate?
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What is the best interpretation for how the porphyritic texture of these rocks formed?
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Ultramafic rocks contain __________ and are commonly found in __________.
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What is an accessory mineral?
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Which of the following best describes the difference between granite and rhyolite?
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What is the rock name of an intermediate rock with two distinct grain sizes?
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What do pumice and scoria have in common?
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Study Notes
Intrusive Igneous Rocks Overview
- Intrusive igneous rocks are exposed through geological processes such as uplift and erosion.
- These rocks form from magma that cools and solidifies beneath Earth's surface.
Types of Intrusive Bodies
- Sills are tabular intrusions that run parallel to sedimentary layers, appearing nearly horizontal.
- Dikes cut across sedimentary layers, exhibiting a nearly vertical orientation.
Timeline of Intrusive Activity
- Magma injections occur below Earth's surface, cutting through sedimentary rock layers.
- Once magma crystallizes, it forms a dike which can resist erosion more than surrounding country rock.
- Erosion eventually exposes intrusive features, leading to significant geological formations.
- Human activities, such as building tunnels, adapt to these resistant igneous structures rather than circumvent them.
Pie Town Dike Observations
- The Pie Town Dike comprises dark fine-grained igneous rock surrounded by paler sedimentary layered sandstones.
- The "baked" margin represents sedimentary rock that underwent thermal alteration due to the close proximity of the magma.
- Observers note that certain sandstone layers demonstrate increased resistance to erosion compared to the dike material.
Igneous Rock Textures
- The cooling rate of magma affects crystal size in igneous rocks: slow cooling creates larger crystals, while rapid cooling results in smaller crystals.
- Porphyritic texture shows a combination of larger crystals in a finer matrix, indicating varying cooling rates during solidification.
Classification of Igneous Rocks
- Ultramafic rocks, primarily containing olivine, are typically found in Earth's mantle.
- Accessory minerals constitute a minor component of a rock's overall mineral makeup.
- Granite is a phaneritic texture rock, while rhyolite is characterized by an aphanitic texture, showing differing crystal sizes.
- Andesite porphyry is identified as an intermediate rock with two distinct grain sizes.
- Pumice and scoria both contain gas bubbles, contributing to their lightweight and porous characteristics.
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Description
Test your knowledge on intrusive igneous rocks with these flashcards focused on Chapter 4 of Geol 1403. Learn about the characteristics and formation of these rocks as well as their relationship with sedimentary structures. Perfect for students looking to reinforce their understanding of igneous geology.
