05. Rocks and Minerals - Rocks A17DE

Heriot-Watt University OverviewCourse: BSc in Physical GeographyModule: A17DE Dynamic Earth 2Session: 4

Topics Covered

  • Rocks & Minerals: This module encompasses an in-depth study of various rock types, their classification, identification, and the processes that lead to their formation and alteration in the Earth's crust.

Coursework Assessment

  • Coursework Type: An assessment covering rock and mineral identification will examine students’ ability to classify rocks and minerals based on their physical and chemical properties, understand Earth’s structure, and explore its geological history.

  • Value: The coursework is significant, accounting for 10% of the overall course mark, emphasizing its importance in the curriculum.

  • Release Date: The assessment materials will be made available on 30th January at 11 am (confirmation pending).

  • Submission Deadline: Completed assessments must be submitted by 6th February at 23:59, although this date is subject to change based on university guidelines.

  • Practical Requirement: Students will engage in hands-on activities working with actual rock and mineral samples prior to the assessment to enhance understanding through real-world applications.

Learning Objectives and Outcomes

Students will:

  1. Understand various kinds of minerals and predict their expected locations in the Earth.

  2. Accurately identify minerals based on their distinguishing properties such as color, hardness, luster, and specific gravity.

  3. Explain the stability of various minerals under surface conditions, considering factors like temperature, pressure, and chemical environments.

  4. Gain insight into the processes involved in rock formation and the continuous rock cycle, including sedimentation and erosion.

  5. Relate specific rock properties to their respective mineral composition and crystalline structure effectively.

  6. Differentiate among various rock types based on distinct physical features and characteristics.

Rocks: Definitions and Characteristics

  • Definition: A rock is defined as an aggregate of one or more minerals, which can manifest as crystalline structures, grains, or even non-crystalline forms.

  • Porosity: The porosity of a rock is a crucial characteristic influenced by the arrangement of clasts or grains, which determines its void space and impacts fluid storage and movement within the rock.

The Rock Cycle

  • Processes: The rock cycle is a comprehensive concept that illustrates the continuous transformation of rocks through various geological processes, including melting, erosion, sedimentation, and metamorphism.

  • Igneous Rocks: These rocks originate from the solidification of molten material (magma or lava). The cooling rate significantly influences the crystallization process, affecting crystal size and structure.

  • Types of Igneous Rocks:

    • Basalt: Characterized by small crystals and a porous texture, formed from rapid cooling of lava on the Earth’s surface (volcanic).

    • Granite: Composed of large crystals due to slower cooling, typically formed intrusively, deep within the Earth’s crust.

Igneous Rock Formation

  • Cooling Processes:

    • Intrusive: Slow cooling allows larger crystals to form, commonly seen in rocks like granite.

    • Extrusive: Rapid cooling results in smaller crystal sizes, characteristic of rocks like basalt.

  • Examples of Composition:

    • Basalt: A mafic rock, silica-poor, often derived from the Earth’s mantle.

    • Granite: A silica-rich rock formed from the melting of continental crust or fractionated mafic magma, showcasing a variety of minerals.

Composition and Properties of Igneous Rocks

  • Phenocrysts: These are larger crystals formed within a finer-grained matrix during magma cooling, providing key insights into the cooling history of the rock.

  • Vesicles: Gas bubbles trapped within volcanic rocks signify rapid cooling and expand during lava eruptions, often resulting in a unique porous texture.

  • Comparative Characteristics: Intrusive rocks, with their larger crystals, provide a striking difference to extrusive rocks, which usually possess smaller crystals.

Classification of Igneous Rocks

  • Mafic: Rich in magnesium and iron, typified by basalt.

  • Intermediate: Contain both mafic and felsic minerals, exemplified by andesite.

  • Felsic: Rich in silicon and aluminum, commonly seen in granite formations.

Metamorphic Rocks

  • Definition: Metamorphic rocks develop from pre-existing igneous or sedimentary rocks that have undergone significant alteration due to extreme heat and pressure.

  • Processes: The metamorphic process involves recrystallization—where minerals change without melting—and results in variations in mineralogy and grain size.

  • Types of Metamorphic Rocks:

    • Slate: Originating from mudstone, exhibiting planar cleavage.

    • Schist: Noted for its pronounced foliation and larger mineral grains.

    • Gneiss: Featuring banding due to differential concentration of minerals.

Types of Metamorphism

  1. Regional Metamorphism: Occurs over extensive areas under elevated temperatures and pressures, often associated with mountain-building processes.

  2. Contact Metamorphism: Takes place adjacent to molten materials, leading to localized alteration of rocks.

  3. Metasomatism: Involves the alteration of rock composition through the introduction of fluids that can change mineralogy without affecting the rock's bulk composition.

Sedimentary Rocks

  • Definition: Formed through the compaction and cementation of particulate sediments, sedimentary rocks provide insights into historical geological environments.

  • Classification: These rocks can be classified into:

    • Clastic: Composed of fragments from other rocks or minerals.

    • Organic: Resulting from the accumulation of biological materials, such as coal.

    • Chemical: Formed through mineral precipitation from solution.

  • Examples of Sedimentary Rocks Include:

    • Conglomerate: A coarse-grained rock made from rounded clasts.

    • Sandstone: A medium-grained rock, commonly utilized in construction due to its durability.

    • Mudstone: Fine-grained with significant clay content, demonstrating significant compression in its formation.

Summary Remarks

In summary, geological studies classify rocks into three primary types: igneous, metamorphic, and sedimentary. Understanding these classifications and their interrelations is essential in grasping the dynamic processes that lead to the formation, alteration, and reformation of rocks over extensive geological timescales.

This comprehensive overview allows students to appreciate the complexity of Earth's materials and processes, equipping them with the knowledge necessary for understanding physical geography in a greater context.