Rocks 3.1 The Rock Cycle  Rocks – naturally occurring, solid mass of minerals  Types of Rocks 1. Igneous rock - formed by the crystallization of molten magma/lava.

3.1 The Rock Cycle Rocks  Types of Rocks 2. Sedimentary rock - formed from weathered products of preexisting rocks that have been transported, deposited, compacted, and cemented. 3. Metamorphic rock - formed by the alteration of preexisting rock deep within Earth (still in the solid state) by heat, pressure, and/or chemically active fluids.

3.1 The Rock Cycle The Rock Cycle  Interrelationships among the three rock types (igneous, sedimentary, and metamorphic)  Magma - molten material deep beneath the Earth’s surface.  Lava - magma that reaches the surface.  Weathering - process in which rocks are broken down by water, air, and living things.  Sediment - weathered pieces of Earth elements.

The Rock Cycle

3.1 The Rock Cycle Energy That Drives the Rock Cycle  Heat from the Earth’s interior forms igneous rock and metamorphic rock.  Weathering and erosion are external processes powered by the sun that form sedimentary rocks.

3.2 Igneous Rocks Formation of Igneous Rocks 1. Intrusive igneous rocks - formed when magma hardens beneath Earth’s surface. 2. Extrusive igneous rocks - formed when lava hardens at Earth’s surface.

3.2 Igneous Rocks Classification of Igneous Rocks  Igneous rocks are classified by composition and texture. 1. Texture • Coarse-grained texture (large crystals) is caused by slow cooling. • Fine-grained texture (small grains) is caused by rapid cooling.

3.2 Igneous Rocks Classification of Igneous Rocks 1. Texture (continued) • Glassy texture is caused by very rapid cooling. • Porphyritic texture is caused by different rates of cooling resulting in varied mineral sizes. 2. Composition • Granitic composition rocks are made mostly of light-colored quartz and feldspar.

3.2 Igneous Rocks Classification of Igneous Rocks 2. Composition (continued) • Basaltic composition rocks are made mostly of dark-colored silicate minerals and plagioclase feldspar. • Andesitic composition rocks are between granitic, light-color minerals and basaltic, dark-colored minerals. • Ultramafic composition rocks are made mostly from iron and magnesium-rich minerals.

Classification of Igneous Rocks

3.3 Sedimentary Rocks Formation of Sedimentary Rocks • Weathering – breakdown of rock Erosion – transport of broken sediments • Deposition - when an agent of erosion—water, wind, ice, or gravity—drops sediments.

3.3 Sedimentary Rocks Formation of Sedimentary Rocks • Compaction - process that squeezes/compacts sediments. • Cementation - when dissolved minerals are deposited in the tiny spaces of sediments.  Features of sedimentary rocks are clues to how and where the rocks are formed

3.3 Sedimentary Rocks Classification of Sedimentary Rocks 1. Clastic sedimentary rocks - composed of weathered bits of rocks and minerals. • Classified by particle size • Common examples: - Shale (most abundant) - Sandstone - Conglomerate

3.3 Sedimentary Rocks Classification of Sedimentary Rocks 2. Chemical sedimentary rocks form when dissolved substances precipitate, or separate, from water. Common rocks include - limestone—most abundant chemical rock - microcrystalline quartz known as chert, flint, jasper, or agate - evaporites such as rock salt or gypsum - coal

Classification of Sedimentary Rocks

3.4 Metamorphic Rocks Formation of Metamorphic Rocks  Metamorphism means “to change form.”  Formation occurs at high temperatures and pressures.  Conditions are found a few km below the Earth’s surface and extend into the upper mantle.

3.4 Metamorphic Rocks Formation of Metamorphic Rocks  Contact metamorphism occurs when magma moves into rock. Occurs near a body of magma Changes are driven by a rise in temperature.

3.4 Metamorphic Rocks Formation of Metamorphic Rocks  Regional metamorphism results in large-scale deformation and high-grade metamorphism. Directed pressures and high temperatures occur during mountain building. Produces the greatest volume of metamorphic rock

3.4 Metamorphic Rocks Agents of Metamorphism  Heat  Pressure Provides the energy needed to drive chemical reactions  Pressure Causes a more compact rock with greater density

3.4 Metamorphic Rocks Agents of Metamorphism  Hydrothermal Solutions Hot water-based solutions escaping from the mass of magma Promote recrystallization by dissolving original minerals and then depositing new ones

3.4 Metamorphic Rocks Classification of Metamorphic Rocks  Two main categories 1. Foliated Metamorphic Rock Has a banded or layered appearance 2. Nonfoliated Metamorphic Rock Does not have a banded texture

Classification of Metamorphic Rocks