The Rock Cycle Study Notes

The Rock Cycle

Objectives of Lecture

• To learn about the parts of the Rock Cycle:

  • Igneous Rocks

  • Sedimentary Rocks

  • Metamorphic Rocks

Definition of Rock

• A naturally occurring group of one or more kinds of minerals.

  • Source: geology.com

Components of the Rock Cycle

• Weathering:

  • The breakdown of rocks into smaller particles.

• Erosion:

  • The wearing away of rocks and soil, transporting sediments elsewhere.

• Transport:

  • Movement of sediment via natural forces (e.g., water, wind).

• Deposition:

  • Sediments settle out of the transporting medium and accumulate.

• Igneous Rocks:

  • Result from the cooling and solidification of melted rock.

  • Lava: Melted rock that reaches the surface of the Earth.

  • Magma: Melted rock located below Earth's surface.

• Sedimentary Rocks:

  • Formed from fragments of other rocks, organic material, or through chemical processes.

• Metamorphic Rocks:

  • Formed by the alteration of existing rocks under heat, pressure, or chemically.

Igneous Rocks

• Definition: Rocks that cool down from melted rock.

  • Lava: Formed on the surface post-eruption.

  • Magma: Formed below the surface.

Categories of Igneous Rocks

1. Extrusive Igneous Rocks:

   • Form on the surface after volcanic eruptions.

   • Cool quickly, resulting in small crystal sizes.

2. Intrusive Igneous Rocks:

   • Form when magma cools underground.

   • Cool slowly, leading to large crystal sizes.

Magma Chambers

• Locations in the upper mantle or lower crust where magma accumulates.

• Characteristics:

  • Partially melted rock.

  • Contain gases that may lead to eruptions.

Volcanoes

• Definition: Openings in the Earth where magma, ash, and gases escape.

• Mechanism of Eruption:

  • As magma rises, it melts and expands, increasing pressure until an eruption occurs.

Types of Volcanoes

1. Composite/Strato Volcano:

   • Constructed from many layers of hardened ash, lava, and pumice.

2. Cinder Cone Volcano:

   • Made of layers of extrusive igneous rock called scoria.

3. Shield Volcano:

   • Primarily composed of lava flows.

   • Features flatter profiles and gently sloping sides.

Types of Eruptions

1. Pyroclastic Eruption:

   • Ejects gas and ash into the atmosphere, characterized by high viscosity silica-rich lava.

2. Lava Flow:

   • Occurs when lava flows over the Earth's surface, typically involving lower viscosity lava.

Textures of Igneous Rocks

• Fine Grained: Indicates rapid cooling characteristic of extrusive rocks.

• Coarse Grained: Indicates slower cooling typical of intrusive rocks.

• Vesicular Texture: Formed when gas escapes from lava.

• Pyroclastic Texture: Produced from ash and rock fragments.

• Glassy Texture: Also known as “vitreous,” formed under specific cooling conditions.

• Porphyritic Texture: Rocks displaying large crystals embedded in a fine-grained matrix; relevant to both intrusive and extrusive types.

Sedimentary Rocks

• Definition: Rocks that form through the accumulation and lithification of sediment, biological material, or through chemical processes.

Components of Sedimentary Rocks

• Made primarily of clasts—pieces of sediment that have been eroded and transported from their original sources.

Formation of Clastic Sedimentary Rocks

1. Weathering/Erosion: Disintegration of rocks into smaller particles.

2. Transport: Movement of sediments through wind, water, or ice.

3. Deposition: Settling of sediments when the transport energy diminishes.

4. Cementation/Lithification: Transformation of sediment into solid rock through compaction and cementation processes.

Weathering Types

1. Chemical Weathering: Dissolving or decomposing earth materials.

2. Physical Weathering: Mechanical breakdown of rocks into smaller particles.

3. Biological Weathering: Breakdown due to biological actions, like tree roots and burrowing organisms.

Erosion Factors

• Caused by:

  • Wind

  • Rivers and Streams

  • Ocean Waves

  • Glacial Activity

  • Gravity

  • Biological activity (Bioerosion).

Sediment Transport Mechanisms

• Rivers, Wind, Waves, and Glaciers.

Sediment Deposition

• Occurs when sediment stops moving, forming layers that may eventually solidify into rock.

• Common settings for deposition: riverbeds, floodplains, deltas, seas, and lakes.

Lithification Process

• Involves compaction and cementation of sediments.

• Compaction: Increased pressure forces clasts close together.

• Cementation: Groundwater leaves mineral deposits, bonding sediment grains.

• Common Cement Types:

  • Carbonate

  • Silica

  • Iron Oxide

Grain Size and Shape

• Visual classification and sorting of grains:

  • Gravel/Pebbles: Course, poorly sorted.

  • Sand: Varies from coarse to fine.

  • Clay: Well-rounded to subangular shapes.

Sorting of Grains

• Determines the degree to which sediments have been sorted during transport:

  • Well-Sorted: Typically formed by wind or water transport.

  • Poorly Sorted: Generally associated with glacial transport.

Examples of Clastic Sedimentary Rocks

• Mudstones, Claystone, Shale, Siltstone, Sandstones, Quartz Sandstone, Lithic Sandstone, Conglomerate, Breccia.

Sedimentary Structures

• Features that develop during deposition:

  • Laminated Bedding

  • Cross-Bedding

  • Ripple Marks

  • Mud Cracks

  • Trace Fossils

  • Presence of fossils or microfossils transforms the rock into “bioclastic” or “biochemical.”

Coal: An Organic Carbon Biochemical Sedimentary Rock

• Formed from ancient plant debris usually found in swamp environments.

• Types include: Bituminous Coal.

Non-Clastic Chemical Sedimentary Rocks

• Formed mineral precipitated from water.

• Examples include:

  • Rock Salt

  • Chert

  • Ironstone

Metamorphic Rocks

• Definition: Rocks transformed from one type to another due to pressure, heat, or both.

  • Changes can be from sedimentary or igneous to metamorphic rocks.

Parent Rock to Daughter Rock Transformations

• Shale ➔ Slate

• Limestone ➔ Marble

Pressure Influences on Metamorphic Rocks

• Understanding pressure types:

  • Lithostatic Pressure: Vertical pressure measured in kilobars (kbar).

  • 1 kbar = 1,000 bars, with atmospheric pressure at sea level being 1 bar.

Factors Influencing Mineral Composition in Metamorphic Rocks

• The primary influences include:

  • Composition of the parent rock.

  • Temperature conditions.

  • Changes in applied pressure.

  • The amount and chemistry of fluids present during metamorphism.

Common Metamorphic Minerals

• Talc, Chlorite, Epidote, Garnet, Actinolite, Serpentine, Chrysotile asbestos, Staurolite, Corundum.

Types of Metamorphism

1. Contact Metamorphism: Results from heat contact with hot magma.

2. Hydrothermal Metamorphism: Involves superheated fluids that alter minerals within the rocks.

3. Burial Metamorphism: Occurs under increasing pressure and heat, preserving sedimentary structures.

4. Regional Metamorphism: Happens during mountain building processes where rocks may fold and deform under applied directed pressure.

5. Other Types:

   • Shock Metamorphism: Results from impact events.

   • Pyrometamorphism: Associated with high-temperature events.

   • Fulgurite: Formation due to lightning strikes.

Textures for Identifying Metamorphic Rocks

• Foliated Textures: Characterized by minerals aligning perpendicularly to stress due to directed pressure.

  • Examples: Slaty Cleavage, Phyllite, Schistocity, Gneissic Banding.

  • Gneiss: Demonstrates banding with alternating light and dark minerals.

• Non-Foliated Textures: Crystalline and microcrystalline textures without apparent layering.

  • Examples: Quartzite (a lower-grade metamorphic rock) and Marble.

Metamorphic Grade

• Low-Grade: e.g., Shale to Slate.

• High-Grade: e.g., Phyllite to Gneiss.

Conclusion

• Review Questions:

  • Name the three types of rock discussed:

  1. Clastic

  2. Punk

  3. Hand

Note: Multiple videos about topics like limestone and metamorphic rocks in the Grand Canyon provide additional resources for understanding these concepts.