Earth Science

Tarbuck/Lutgens

Earth ScienceEarth Science

Rocks:

Earth’s

Materials

Chapter 3

Chapter-3 Rocks PretestChapter-3 Rocks Pretest

1. Describe the strength of bonds between atoms in a solid.

2. What is a mineral?

3. True or False: Only eight elements make up the bulk of the minerals found in Earth’s crust.

4. What is the most common mineral group?

5. What are rock-forming minerals?

6. What are some common properties of minerals?

Rocks Rocks

A rock is any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet.Some rocks are composed of one mineral,

however most rocks are a solid mixture of many minerals.

The three major types of rocks are igneous rocks, sedimentary rocks, and metamorphic rocks.

Rock cycle Rock cycle

Shows the interrelationships among the three rock types.It shows that interactions among Earth’s

water, air, and land can cause rocks to change from one type to another.

Earth as a system: the rock cycle • Magma

• Crystallization of magma or lava

• Igneous rock • Weathering, transportation, and deposition

Rock cycle Rock cycle

Earth as a system: the rock cycle • Sediment

• Lithification

• Sedimentary rock • Metamorphism

• Metamorphic rock • Melting

• Magma

Rock cycle Rock cycle

Earth as a system: the rock cycle • Full cycle does not always take place due to

“shortcuts” or interruptions (alternate paths)• e.g., Sedimentary rock melts • e.g., Igneous rock is metamorphosed • e.g., Sedimentary rock is weathered • e.g., Metamorphic rock weathers

The

Rock Cycle

Igneous rocksIgneous rocks

Form as magma cools and crystallizes • Rocks formed inside Earth

are called plutonic or intrusive rocks

• Rocks formed on the surface

• Formed from lava (a material similar to magma, but without gas)

• Called volcanic or extrusive rocks

Igneous RocksIgneous Rocks

Igneous rocks Igneous rocks

Crystallization of magma • Ions are arranged into orderly patterns • Crystal size is determined by the rate of

cooling • Slow rate forms large crystals • Fast rate forms microscopic crystals • Very fast rate forms glass

Igneous rocks Igneous rocks

Classification is based on the rock’s texture and mineral constituents • Texture

• Size and arrangement of crystals • Types

• Fine-grained – fast rate of cooling• Coarse-grained – slow rate of cooling • Porphyritic (two crystal sizes) – two rates of

cooling • Glassy – very fast rate of cooling

Fine-grained igneous Fine-grained igneous texturetexture

Coarse-grained igneous Coarse-grained igneous texturetexture

Porphyritic igneous Porphyritic igneous texturetexture

Obsidian exhibits a Obsidian exhibits a glassy textureglassy texture

Composition of MagmaComposition of Magma

• Silica (SiO2) is the most abundant compound found in magma and has the greatest effect on magma characteristics.– Silica content affects:

• Melting temperature• Speed at which magma

flows

Origins of MagmaOrigins of Magma

• Most rocks melt between 800oC and 1200oC– Sources of Earth’s heat

comes from:• Earth’s formation

• Radioactive elements

• Gravitational pull

• Factors affecting magma formation– Temperature

• Temperature increases with depth

Origins of MagmaOrigins of Magma

• Factors affecting magma formation (continued)– Pressure

• Pressure increases with depth

• As pressure increases, its melting point also increases

– Water Content• As water content

increases, the melting point decreases

– Mineral Content• Different minerals have

different melting points

Origins of MagmaOrigins of Magma

• How Rocks Melt– Partial Melting

• Process whereby some minerals melt at low temperatures while others remain solid

– Magma chemistry can change if it partially melted

Origins of MagmaOrigins of Magma

• How Rocks Melt– Fractional Crystallization

• Process wherein different minerals form at different temperatures

Igneous rocks Igneous rocks

Classification is based on the rock’s texture and mineral constituents • Mineral composition

• Explained by Bowen’s reaction series which shows the order of mineral crystallization

• Influenced by crystal settling in the magma

Bowen’s reaction seriesBowen’s reaction series

Origins of MagmaOrigins of Magma

• Crystal Separation– Occurs when crystals settle

to the bottom of the magma body, or when liquid magma is separated from the magma body

• Layered Intrusions– In some magma bodies,

the minerals form into distinct bands in the order shown in Bowen’s Reaction Series

Classification of Classification of igneous rocksigneous rocks

Classification of Classification of igneous rocksigneous rocks

Igneous rocks Igneous rocks

Naming igneous rocks • Granitic rocks

• Composed almost entirely of light-colored silicates – quartz and feldspar

• Also referred to as felsic: feldspar and silica (quartz)

• High silica content (about 70 percent) • Common rock is granite

GraniteGranite

Igneous rocks Igneous rocks

Naming igneous rocks • Basaltic rocks

• Contain substantial dark silicate minerals and calcium-rich plagioclase feldspar

• Also referred to as mafic: magnesium and ferrum (iron)

• Common rock is basalt

Basalt Basalt

Igneous rocks Igneous rocks

Naming igneous rocks • Other compositional groups

• Andesitic (or intermediate) • Ultramafic

End of Chapter 3End of Chapter 3Sections 1 & 2Sections 1 & 2