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Questions and Answers
What is the characteristic of hypabyssal rocks in terms of their grain size?
What is the characteristic of hypabyssal rocks in terms of their grain size?
Which type of igneous rocks is characterized by a phaneritic texture?
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 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?
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?
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?
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?
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?
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?
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?
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.
