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Questions and Answers
What is the term used to describe the sizes and shapes of a rock's mineral crystals or grains?
What is the term used to describe the sizes and shapes of a rock's mineral crystals or grains?
- Geologic origin
- Texture (correct)
- Aggregate
- Mineralogy
Which type of rock is made up of compacted plant remains?
Which type of rock is made up of compacted plant remains?
- Coal (correct)
- Pumice
- Volcanic
- Obsidian
What determines a rock's appearance, including its mineralogy and texture?
What determines a rock's appearance, including its mineralogy and texture?
- Size of crystals
- Geologic origin (correct)
- Colour variation
- Aggregate composition
Which type of rocks can include noncrystalline, glassy volcanic rocks?
Which type of rocks can include noncrystalline, glassy volcanic rocks?
In the Barrovian sequence, how are metamorphic grades classified?
In the Barrovian sequence, how are metamorphic grades classified?
What does metamorphic facies correspond to?
What does metamorphic facies correspond to?
How are metamorphic rocks classified when the protolith cannot be determined?
How are metamorphic rocks classified when the protolith cannot be determined?
What does metamorphic grade indicate?
What does metamorphic grade indicate?
At what temperature does metamorphism take place?
At what temperature does metamorphism take place?
What is the term for the metamorphism occurring at increasing pressure and temperature conditions?
What is the term for the metamorphism occurring at increasing pressure and temperature conditions?
What effect does pressure have on a rock's chemical composition, mineralogy, and texture?
What effect does pressure have on a rock's chemical composition, mineralogy, and texture?
Which classification system is used to name volcanic rocks based on the combined alkali content and silica content?
Which classification system is used to name volcanic rocks based on the combined alkali content and silica content?
In which scenario is the TAS classification preferred over QAPF diagrams for classifying volcanic rocks?
In which scenario is the TAS classification preferred over QAPF diagrams for classifying volcanic rocks?
Why is it difficult to assign an exact name to a plutonic rock in the field?
Why is it difficult to assign an exact name to a plutonic rock in the field?
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Study Notes
Rock Properties and Composition
- Term for Crystal Size and Shape: The sizes and shapes of a rock's mineral crystals or grains are referred to as texture.
- Compact Plant Remains: Coal is the type of rock formed from compacted plant remains.
- Determination of Rock Appearance: A rock's appearance, including its mineralogy and texture, is determined by its composition and formation process.
Classification of Rocks
- Glassy Volcanic Rocks: Igneous rocks can include noncrystalline, glassy types, such as obsidian.
- Barrovian Sequence: In the Barrovian sequence, metamorphic grades are classified based on increasing metamorphic conditions, ranging from low to high grade.
- Metamorphic Facies: Metamorphic facies correspond to specific pressure and temperature conditions that create distinct mineral assemblages.
Metamorphic Rock Characteristics
- Classification Without Protolith: When the protolith cannot be determined, metamorphic rocks are classified using textural characteristics and mineral composition.
- Metamorphic Grade Indication: Metamorphic grade indicates the intensity of temperature and pressure conditions a rock has undergone.
- Temperature for Metamorphism: Metamorphism typically takes place at temperatures greater than 200°C.
Metamorphism and Pressure
- Increasing Pressure and Temperature Metamorphism: The term for metamorphism occurring at increasing pressure and temperature conditions is termed regional metamorphism.
- Effect of Pressure: Increased pressure affects a rock's chemical composition, mineralogy, and texture by promoting densification and promoting new mineral formation.
Volcanic Rock Classification Systems
- Classification System for Volcanic Rocks: The TAS (Total Alkali-Silica) classification system is used to name volcanic rocks based on alkali and silica content.
- TAS Preference: TAS classification is preferred when the rock is composed of highly differentiated volcanic rocks where silica content varies extensively.
- Naming Plutonic Rocks Difficulty: Assigning an exact name to plutonic rocks in the field is challenging due to variability in mineral composition and the effects of weathering.
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