10 Questions
What is the primary factor that determines the chemical composition of a rock?
The kind of constituent minerals present in the rock
What is the term for the process by which rocks are formed by solidification and crystallization from liquid rock?
Igneous formation
What is the difference between volcanic and intrusive igneous rocks?
Their location of formation
What is the term for the mixture of liquid rock, crystals, and gas that forms igneous rocks?
Magma
What is the primary reason why magmas are able to move upward through the surrounding rocks?
Because they are less dense than the surrounding rocks
What is the term for the process by which sedimentation of mineral and rock fragments occurs?
Sedimentation
What is the term for rocks that are formed by increasing the pressure and/or temperature on a previously existing rock?
Metamorphic rocks
What is the term for the classification of rocks based on their geological formation process?
Geological classification
What is the characteristic of rocks that is used to distinguish between monomineralic and polymineralic rocks?
Number of minerals
What is the term for the study of the formation and composition of igneous rocks?
Igneous petrology
Study Notes
Igneous Rocks Classification
- Igneous rocks can be classified based on silica percentage and depth of formation
- Four main groupings of igneous rocks based on silica percentage:
- Acid (Felsic) - more than 66% silica
- Intermediate - 52-66% silica
- Basic (Mafic) - 45-52% silica
- Ultrabasic (Ultramafic) - less than 45% silica
Characteristics of Igneous Rocks
- Acid Igneous Rocks:
- Rich in silica (more than 66%)
- Minerals: quartz, orthoclase, sodium-plagioclase, muscovite, and biotite
- Low melting temperatures
- Intermediate Igneous Rocks:
- Silica content: 52-66%
- Minerals: quartz, orthoclase, plagioclase, biotite, hornblende, and augite
- Basic Igneous Rocks:
- Silica content: 45-52%
- Minerals: calcium-plagioclase, augite, olivine, and hornblende
- Ultrabasic Igneous Rocks:
- Silica content: less than 45%
- Minerals: calcium-plagioclase, olivine, and augite
- No feldspars or quartz
Depth of Formation
- Plutonic: formed at considerable depth within the crust, slow cooling, coarse-grained texture
- Hypabyssal: formed as small bodies of rock, medium-grained texture
- Volcanic: formed at the planetary surface, rapid cooling, fine-grained texture
Structures of Igneous Rocks
- Plutons: large intrusive bodies that intrude and replace rocks in an irregular fashion
- Stocks: smaller bodies that are likely fed from deeper level batholiths
- Batholiths: formed when multiple intrusive events occur in the same part of the crust
Rates of Cooling and Igneous Textures
- Fast cooling: aphanitic texture or obsidian (volcanic glass)
- Slow cooling: phaneritic texture
- Porphyritic texture: develops when slow cooling is followed by rapid cooling
- Phenocrysts: larger crystals
- Matrix or groundmass: smaller crystals
Classification of Igneous Rocks
- Two main types: based on silica percentage and depth of formation
Learn about the classification of igneous rocks based on their silica content and mineral composition. Understand the characteristics of light-colored, intermediate, and basic igneous rocks.
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