Earth Science: Classification of Rocks

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Questions and Answers

What is the term used for the larger crystals found in igneous rocks?

Glassy texture

Groundmass

Phenocryst (correct)

Matrix

Which type of igneous rock is characterized by a high percentage of quartz and a light color?

Intermediate

Felsic (correct)

Ultramafic

Mafic

Which term describes noncrystalline rocks that contain no mineral grains?

Vitreous

Porphyritic

Vesicular texture

Glassy texture (correct)

What causes vesicular texture in igneous rocks?

Decreasing pressure during magma ascent Signup and view all the answers

What mineral accounts for up to 60% of the composition of granite?

Feldspar Signup and view all the answers

What is the primary factor that influences the size of mineral crystals in igneous rocks?

The rate of cooling of magma Signup and view all the answers

Which characteristic distinguishes extrusive igneous rocks from intrusive igneous rocks?

They cool rapidly on the Earth's surface Signup and view all the answers

What type of texture do rocks like granite exhibit?

Phaneritic texture Signup and view all the answers

Which of the following rocks would be classified as having a fine-grained or aphanitic texture?

Basalt Signup and view all the answers

Which of the following statements about the cooling of magma is incorrect?

Slow cooling creates smaller crystals. Signup and view all the answers

What kind of igneous rock forms when magma cools and solidifies beneath the Earth's surface?

Intrusive rock Signup and view all the answers

Which term describes rocks with a significant difference in grain size?

Porphyritic Signup and view all the answers

What does the term 'crystallization' refer to in the context of igneous rocks?

The cooling and solidification of magma Signup and view all the answers

What process primarily leads to the formation of evaporites?

Evaporation of water leaving dissolved minerals Signup and view all the answers

Which type of metamorphism is primarily driven by heat and reactive fluids?

Contact metamorphism Signup and view all the answers

What characterizes bioclastic rocks?

Formed from compacted organic matter Signup and view all the answers

What is a common result of regional metamorphism?

Mechanical deformation and chemical recrystallization Signup and view all the answers

Which rock type is NOT typically formed through the process of metamorphism?

Granite Signup and view all the answers

What is the primary effect of compaction on sediment grains?

It reduces pore space and eliminates water. Signup and view all the answers

What characterizes graded bedding in sedimentary rocks?

Larger particles are deposited before smaller ones. Signup and view all the answers

Which sedimentary feature is created by drying wet sediment?

Mudcracks. Signup and view all the answers

What does the term 'mafic' refer to in geology?

Rocks rich in magnesium and iron Signup and view all the answers

What type of sedimentary rock is primarily formed through evaporation?

Halite. Signup and view all the answers

What is indicated by the presence of fossils in sedimentary rocks?

The environment of deposition. Signup and view all the answers

Which minerals are typically associated with ultramafic rocks?

Olivine and pyroxene Signup and view all the answers

In Bowen's Reaction Series, what is primarily observed in the discontinuous reaction series?

Increasing silica content as temperature decreases Signup and view all the answers

How are clastic sedimentary rocks primarily classified?

By particle size. Signup and view all the answers

What is the first step in the formation of sedimentary rocks?

Weathering Signup and view all the answers

Which of the following is NOT classified as a non-clastic sedimentary rock?

Quartz sandstone. Signup and view all the answers

What characterizes the continuous reaction series in Bowen’s Reaction Series?

Changes in composition from sodium to calcium as temperature decreases Signup and view all the answers

What type of sedimentary structure involves beds inclined relative to one another due to current movement?

Cross bedding. Signup and view all the answers

During lithification, which process initially occurs to sediment?

Compaction Signup and view all the answers

Which step in the sedimentary processes involves the movement of weathered products?

Erosion Signup and view all the answers

Which type of rock is identified as andesitic or intermediate?

Rocks with a mixture of light and dark minerals Signup and view all the answers

Study Notes

ROCKS AND MINERALS

Rocks are natural, solid, nonliving materials composed of one or more minerals.
Minerals are the building blocks of rocks.

TYPES OF ROCKS

Rocks are classified into three major types: igneous, sedimentary, and metamorphic.

IGNEOUS ROCK

Derived from the Latin word for "fire."
Formed from the cooling and solidification of magma.
Crystal size depends on cooling time: slow cooling produces large crystals, rapid cooling creates small crystals.

Main Categories

Extrusive Igneous Rocks (Volcanic)
- Form on the Earth's surface from lava.
- Generally have small crystals due to rapid cooling, known as aphanitic texture.
Intrusive Igneous Rocks (Plutonic)
- Form below the Earth's surface from magma that cools slowly.
- Characterized by large, visible crystals, known as phaneritic texture.

TEXTURE OF IGNEOUS ROCKS

Coarse Grained (Phaneritic)
- Large, visible crystals; examples include granite, gabbro, and diorite.
Fine-Grained (Aphanitic)
- Small, invisible crystals; example includes basalt.
Porphyritic Texture
- Contains two different crystal sizes, with phenocrysts (larger) in a finer groundmass.
Glassy Texture (Vitreous)
- Non-crystalline rocks with no mineral grains, such as obsidian.
Vesicular Texture
- Formed by gas bubbles from rising magma, resulting in a porous appearance.

CHEMICAL COMPOSITION OF IGNEOUS ROCKS

Felsic Rocks
- Light-colored, high in feldspar and quartz.
Mafic Rocks
- Dark-colored, rich in magnesium and iron; example includes basalt.
Andesitic (Intermediate) Rocks
- Contain a mix of light and dark minerals like amphibole and plagioclase feldspar.
Ultramafic Rocks
- Composed mainly of dark minerals such as olivine.

BOWEN’S REACTION SERIES

Describes the crystallization process of magma.
Discontinuous Series: Minerals crystallize in steps (e.g., olivine, pyroxene).
Continuous Series: Plagioclase minerals range from calcium-rich at high temperatures to sodium-rich at low temperatures.

SEDIMENTARY ROCKS

Formed from the accumulation of sediments or pre-existing rocks.
Commonly develop at or near the Earth's surface through sedimentary processes.

SEDIMENTARY PROCESSES

Weathering: Breakdown of rocks into smaller fragments.
Erosion: Movement of weathered materials.
Transportation: Sediment movement via wind, water, or gravity.
Deposition: Occurs when energy decreases, allowing sediments to settle.
Lithification: Converts sediment into rock, primarily through compaction.

COMMON SEDIMENTARY FEATURES

Stratification and Bedding: Layers of sediment.
Cross Bedding: Inclined layers formed by water or wind movement.
Graded Bedding: Layering characterized by decreasing grain size.
Ripple Marks: Formed by flowing water over sediments.
Mudcracks: Result from drying sediments.
Fossils: Indicators of past life and depositional environments.

TYPES OF SEDIMENTARY ROCKS

Clastic: Composed of grains, classified by particle size (e.g., sandstone, shale, conglomerate).
Non-Clastic: Formed by evaporation/precipitation of minerals or lithification of organic matter (e.g., limestone, coal).

METAMORPHIC ROCKS

Formed from existing rocks due to pressure and temperature changes during metamorphism.

Types of Metamorphism

Contact Metamorphism
- Involves heat and reactive fluids from nearby magma, creating non-foliated rocks.
Regional Metamorphism
- Occurs under high pressure and extensive deformation, typically during mountain-building events.

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Description

This quiz covers the classification of rocks, focusing on igneous rocks and their formation from magma. Learn about the characteristics and processes involved in rock formation. Ideal for Earth Science students looking to deepen their understanding of geology.