earth and life science

Exploring Types of Rocks in Earth & Life Science

Learning Objectives

  • Identify and differentiate between intrusive and extrusive igneous rocks.

  • Describe the formation process of the 3 types of rocks.

  • Identify common examples of each type of rock.

Overview of Rocks

  • Earth is composed of solid rock extending to a depth of 2,900 kilometers.

  • Petrology: The scientific study of rocks.

Classification of Rocks

Rocks are classified into three main types based on their formation:

  1. Igneous Rocks

  2. Sedimentary Rocks

  3. Metamorphic Rocks

Igneous Rocks

  • Formed from the cooling and solidification of magma or lava.

  • They can be found deep within the Earth or on its surface.

  • Exhibits a variety of colors, textures, and sizes depending on their cooling rate.

Types of Igneous Rocks

  1. Extrusive (Volcanic) Rocks

    • Form when lava cools quickly on Earth's surface.

    • Result in small, fine-grained crystals.

  2. Intrusive (Plutonic) Rocks

    • Form when magma cools slowly beneath the Earth's surface.

    • Exhibit large, coarse-grained crystals.

Classification Criteria for Igneous Rocks

  1. Composition

    • Felsic: Light colored, silica-rich rocks (e.g., Granite).

    • Mafic: Dark-colored, low-silica rocks (e.g., Basalt).

    • Intermediate: Rocks with balanced silica content.

    • Ultramafic: Very dense, very low-silica content (e.g., Obsidian).

  2. Texture

    • Aphanitic: Fine-grained rocks visible under a microscope.

    • Phaneritic: Coarse-grained rocks with large crystals.

    • Porphyritic: Mixed texture with varying crystal sizes.

    • Glassy: Gas-like texture with no crystals (e.g., Obsidian).

    • Pyroclastic: Formed from explosive volcanic activity.

Examples of Igneous Rocks

  • Diorite, Andesite, Granite, Basalt, Pegmatite, Pumice, Tuff, Scoria, Obsidian.

Metamorphic Rocks

  • Formed from the transformation of existing rocks (igneous or sedimentary) due to heat, pressure, or fluids within the Earth's crust.

  • They often display distinct textures and patterns.

Metamorphism Process

  • Metamorphism: The process of physical and chemical changes without melting.

Types of Metamorphism

  1. Contact Metamorphism: Involves heating by nearby magma, affecting a small area.

  2. Regional Metamorphism: Changes occur over a large region of the crust due to pressure and temperature changes.

Examples of Metamorphic Rocks

  • Common metamorphic rocks include Marble, Slate, Phyllite, and Schist.

Classification of Metamorphic Rocks

  • Texture: Size, arrangement, and shape of grains.

    • Foliation: Planar arrangement of mineral grains or structural features.

  • Types of Foliated and Non-foliated Rocks:

    • Foliated Rocks: Layered appearance (e.g., Gneiss).

    • Non-foliated Rocks: Form under uniform pressure (e.g., Marble).

Sedimentary Rocks

  • Develop from the accumulation and compression of sediment layers (e.g., sand, mud, flora, and fauna).

  • These layers solidify over time to form sedimentary rocks.

Types of Sedimentary Rocks

  1. Clastic Sedimentary Rocks: Formed from clasts' accumulation (e.g., Breccia).

  2. Chemical Sedimentary Rocks: Precipitated from mineral solutions.

  3. Organic Sedimentary Rocks: Formed from accumulated biological debris (e.g., Limestone, Coal).

Trivia

  • The oldest known rocks, the Acasta Gneiss in Canada, are approximately 4 billion years old, nearly as old as Earth itself!