Chapter 3 Rocks

Rocks 3.1 The Rock Cycle Rocks are any solid mass of mineral or mineral-like matter occurring naturally as part of our planet. A rock is a hard substance composed of one or more minerals.

Most common rocks are made from the most abundant elements in the Earth’s crust. Those elements are: Oxygen Aluminum Iron Potassium Silicon Calcium Sodium Magnesium

http://www.youtube.com/watch?v=pg_jKJFbA2A

 Types of Rocks Igneous rock Rocks are placed into groups based upon how they are formed and texture. Igneous rock Formed when liquid magma cools and hardens Get their name from the Latin word ignis – means fire Examples include – granite, basalt, pumice

Pumice Granite

2. Sedimentary rock Formed from other rocks or minerals already present on or very near the Earth’s surface. Formed from particles that have been carried along and deposited by wind and water. The erosion by wind and water creates sediments. Sediments can be bits of rock like mud, sand or pebbles. They can also be shells, bones, leaves, stems and other remains of living things.

Sediments become cemented together to form rocks over time. Sedimentary rocks can be formed as layer of sediments are deposited on the ocean floor. The layers can be exposed when seas are drained or movements in Earth’s crust lift them up. Examples include – sandstone, shale, breccia, limestone

Sandstone Shale Limestone Breccia

3. Metamorphic rock Formed under very intensive heat and pressure for an extended period of time. Formed when chemical reactions, tremendous heat and/or great pressure turn existing rock into new kinds of rocks. This process of change may cause the minerals within the rock to separate into layers forming distinctive bands.

The new rocks have physical and chemical properties that are very different from the original rocks. Examples include – quartzite, schist, marble

Quartzite Schist Marble

http://www.youtube.com/watch?v=lE3jR_RhxO4

3.1 The Rock Cycle The continuous changing of rocks from one kind to another over long periods of time. Shows the interrelationships among the three rock types (igneous, sedimentary, and metamorphic) Magma is molten material that forms deep beneath the Earth’s surface. Lava is magma that reaches the surface. Weathering is a process in which rocks are broken down by water, air, and living things. Sediment is weathered pieces of Earth elements.

Rock Formation and Rock Cycle Animation The rock cycle has no definite sequence. It can follow many pathways.   All rock begins as magma. The magma is extruded (forced out) onto the Earth’s surface and cools or it is cooled within the Earth.

http://www.youtube.com/watch?v=53lMdHzvGCQ

The Rock Cycle

3.1 The Rock Cycle Energy That Drives the Rock Cycle Energy that drives the rock cycle comes from internal and external (sun) processes Processes driven by heat from the Earth’s interior are responsible for forming both igneous rock and metamorphic rock. Weathering and the movement of weathered materials are external processes powered by energy from the sun. External processes produce sedimentary rocks.

How could metamorphic or igneous rock become sedimentary rock? The Rock Cycle Under the right conditions, any type of rock can become another type of rock. How could metamorphic or igneous rock become sedimentary rock? Weathering and erosion break the rocks down into sediments which over time compact and cement to form sedimentary rock.

How could metamorphic or sedimentary rock become igneous rock? If metamorphic or sedimentary rocks melt and then cool, they become igneous rocks.

How could igneous or sedimentary rock become metamorphic rock? When igneous or sedimentary rock undergo extreme heat and/or pressure, they become metamorphic rock

3.2 Igneous Rocks Igneous rocks form from the cooling of molten material. Igneous rocks are classified according to their composition and texture. Composition refers to the minerals that form the rock. Texture is the shape, size, arrangement and distribution of the minerals. Texture and composition are evident in the appearance of the rock. Example: Light colored igneous rocks are usually rich in quartz. Dark colored igneous rocks are usually rich in augite (dense, greenish gray)

http://www.youtube.com/watch?v=mxbmvG5gpAs

3.2 Igneous Rocks Intrusive igneous rocks Magma cooled slowly beneath the Earth’s surface Large crystals form. Course grained Examples – granite  

3.2 Igneous Rocks 2. Extrusive igneous Magma reaches the surface by volcanoes and is cooled there. Fine grained because they cool quickly Produces small sized crystals Also called volcanic rocks Examples – obsidian, basalt and pumice Pumice is so filled with bubbles that it can float

3.2 Igneous Rocks Classification of Igneous Rocks  Igneous rocks can be classified based on their composition and texture. 1. Texture • Coarse-grained texture is caused by slow cooling resulting in larger crystals. • Fine-grained texture is caused by rapid cooling resulting in smaller, interconnected mineral grains.

Course-Grained Igneous Texture

Fine-Grained Igneous Texture

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 sized minerals. 2. Composition • Granitic composition rocks are made mostly of light-colored quartz and feldspar.

Obsidian Exhibits a Glassy Texture.

Porphyritic Igneous Texture

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 composition dark-colored minerals. • Ultramafic composition rocks are made mostly from iron and magnesium-rich minerals.

Basalt

How and where magma cools and the mineral composition determines the size of a minerals crystals. Slow cooling magma produces larger crystals. Glassy and fine grained rocks form when lava erupts from volcanoes and hardens on Earth’s surface. Course grained rocks form when molten rock cools and hardens within the Earth.

Classification of Igneous Rocks

3.3 Sedimentary Rocks Formation of Sedimentary Rocks  Weathering, Erosion, and Deposition • Erosion involves the weathering and the removal of rock. • Deposition occurs when an agent of erosion—water, wind, ice, or gravity—loses energy and drops sediments.

3.3 Sedimentary Rocks Formation of Sedimentary Rocks  Compaction and Cementation • Compaction is a process that squeezes, or compacts, sediments. • Cementation takes place when dissolved minerals are deposited in the tiny spaces among the sediments.

http://www.youtube.com/watch?v=eOuPsJwYu9I

3.3 Sedimentary Rocks Classification of Sedimentary Rocks  Two Main Groups 1. Clastic sedimentary rocks are composed of weathered bits of rocks and minerals. • Classified by particle size • Common rocks include - Shale (most abundant) - Sandstone - Conglomerate

Shale with Plant Fossils

Conglomerate

http://www.youtube.com/watch?v=202gSE4NBWE

3.3 Sedimentary Rocks Classification of Sedimentary Rocks  Two Main Groups 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

Fossiliferous Limestone

Classification of Sedimentary Rocks

3.3 Sedimentary Rocks Features of Some Sedimentary Rocks  Features of sedimentary rocks are clues to how and where the rocks are formed

3.4 Metamorphic Rocks Formation of Metamorphic Rocks  Metamorphism means “to change form.”  Most metamorphic changes occur at elevated temperatures and pressures.  Conditions for formation are found a few kilometers below the Earth’s surface and extend into the upper mantle.

http://www.youtube.com/watch?v=e15n7-zq0mA

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

Origin of Pressure in Metamorphism

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

Gneiss Typically Displays a Banded Appearance

Marble—A Nonfoliated Metamorphic Rock