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Questions and Answers
What is the characteristic of hypabyssal rocks in terms of their grain size?
Which type of igneous rocks is characterized by a phaneritic texture?
What is the primary reason for the development of a porphyritic texture in igneous rocks?
What is the term for the well-formed crystals visible to the naked eye in a porphyritic texture?
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Which type of rock is characterized by a fine-grained or glassy matrix?
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What is the primary difference between a phaneritic and a porphyritic texture?
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What is the characteristic of plutonic rocks in terms of their grain size?
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What is the term for the slow cooling and crystallization of magma within the Earth's crust?
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Which type of rock is characterized by a medium-grained texture?
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What is the primary difference between a hypabyssal and a volcanic rock?
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Study Notes
Igneous Rocks
- Igneous rocks are the most abundant type of rocks, also known as primary rocks.
- They are formed from magma, a hot, partially molten mixture of solid, liquid, and gas.
Magma vs. Lava
- Magma is molten rock beneath the surface.
- Lava is molten rock that has reached the surface.
Composition of Magma
- Composition varies widely.
- Oxygen plus major elements.
- Generally a silica (SiO2) melt.
- Silica and water content control viscosity.
- Silica content is used in classification.
Types of Magma
- Mafic magma:
- Silica content ~ 50%.
- High Fe, Mg, and Ca.
- High temperature molten magma (1000 to 1200°C).
- Major minerals: Olivine, Ca, Plagioclase, and Pyroxene.
- Silicic magma:
- Silica content: 65-77%.
- High Al, Na, and K.
- Lower temperature magmas (<850°C).
- Major minerals: Feldspars, Mica, and Quartz.
Igneous Rocks
- Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of the planet.
- Extrusive igneous rocks are formed on the surface of the Earth from lava.
Forms of Igneous Rocks
- Intrusive igneous rocks:
- Concordant: Sills, Laccoliths, Lopoliths, Phacoliths.
- Discordant: Dykes, Stocks, Volcano Necks, Batholiths.
- Extrusive igneous rocks:
- Lava flows.
- Pyroclasts.
Classification of Igneous Rocks
- Based on the depth of formation/mode of occurrence:
- Plutonic (intrusive): formed under great pressure and high temperature.
- Hypabyssal: formed at shallow depths under moderate temperature and pressure.
- Volcanic (extrusive): formed near the surface of the Earth under low pressure and absence of volatiles.
Textures of Igneous Rocks
- Phaneritic: large, easily visible, interlocking crystals of several minerals.
- Porphyritic: well-formed crystals (phenocrysts) set in a very fine-grained or glassy matrix (groundmass).
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Description
Test your knowledge on igneous rocks, including their forms, classifications, structure, and suitability for building and foundation. Learn about the different types of igneous rocks and their characteristics.
