Chapter

33 TYPES OF:

Rocks

Rocks

Rocks are any solid mass of mineral or mineral-like matter occurring naturally as a part of our planet.

Types of Rocks

• The 3 kinds of rocks are igneous, sedimentary, and metamorphic

Igneous Rocks

• formed by the crystallization of molten magma or lava.

• Magma is molten material deep beneath the Earth’s surface

• Lava is molten material above the surface

Types of Igneous Rocks

1. Intrusive igneous rocks are formed when magma hardens beneath Earth’s surface.

2. Extrusive igneous rocks are formed when lava hardens (above the Earth’s surface).

1. Texture

Igneous rocks can be classified based on their composition and 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.

How Igneous Rocks are Classified

• Glassy texture is caused by very rapid cooling.

Course-Grained Igneous Texture

Granite

Fine-Grained Igneous Texture

Rhyolite

Obsidian Exhibits a Glassy Texture.

2. Composition• What the rock is made of, based on the

amounts of light and dark minerals in the rock.

Porphyritic Igneous Texture

Basalt

Classification of Igneous Rocks

Formation of Sedimentary Rocks

Sedimentary Rocks

• 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.

Sedimentary Rock Formation

• Compaction is a process that squeezes, or compacts, sediments.

• Cementation takes place when dissolved minerals are deposited in the tiny spaces among the sediments.

3 Types of Sedimentary Rock

• Clastic – composed of weathered bits of rocks and minerals– Classified by particle size– Ex: Shale, Sandstone, Conglomerate, Grand

canyon & the wave in Arizona

Shale with Plant Fossils

Sandstone

Conglomerate

The Wave, Page, AZ

Grand Canyon, Arizona

• Chemical – When minerals dissolve out of water– Ex: limestone (caves), coal, rock salt

Fossiliferous Limestone

Carlsbad Caverns, NM

Stalactites

Stalagmites

• Organic – Formed by fossils or organic matter within the rock layers

Classification of Sedimentary Rocks

Formation of Metamorphic Rocks

Metamorphic Rocks

Metamorphism means “to change form.”

Igneous and sedimentary rocks change at elevated temperatures and pressures deep within the Earth or during mountain building

Agents of Metamorphism

Heat

Pressure

• Provides the energy needed to drive chemical reactions

• Causes a more compact rock with greater density

Origin of Pressure in Metamorphism

• Hot water-based solutions escaping from magma

• Dissolves original minerals and then deposits new ones

Hydrothermal Solutions

Classifying Metamorphic Rocks

1. Foliated Metamorphic Rock

2. Nonfoliated Metamorphic Rock

Two main categories

• Has a banded or layered appearance

• Does not have a banded texture

Classification of Metamorphic Rocks

Gneiss Typically Displays a Banded Appearance

Marble—A Nonfoliated Metamorphic Rock

IGNEOUS ROCKS SEDIMENTARY ROCKS

METAMORPHIC ROCKS

     

     

     

     

     

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