What are igneous rocks?What are igneous rocks?

SWBAT compare and contrast intrusive and SWBAT compare and contrast intrusive and extrusive igneous rocks; describe the extrusive igneous rocks; describe the

composition of magma; discuss the factors composition of magma; discuss the factors that affect how rocks melt and crystallize that affect how rocks melt and crystallize

Get your lab notebookGet your lab notebook

• Write a description of the rocks you are shown:• Using the hand lens take a closer look, and

describe what you see:• Draw a picture of what you saw through the

hand lens.• How many different minerals did you see?• What minerals can you identify?• Do you see any evidence that these minerals

crystallized form molten rock? Explain.

How are igneous rocks formed?How are igneous rocks formed?

• Magma– Molten rock under Earth’s surface

• Lava– Magma that flows out onto Earth’s surface

• Igneous rocks are formed when magma cystalizes

Types of Igneous RocksTypes of Igneous Rocks

• Extrusive– Rocks that form from lava solidifying on

Earth’s surface– They are generally fine grained due to quick

cooling

• Intrusive– Rocks that form from magma cooling

underground– Generally coarser grained because of the

longer cooling time

MagmaMagma• What is magma composed of?

– Slushy mix of molten rock, gases, and mineral crystals

• What elements does it contain?– Oxygen, silicon, aluminum, iron, magnesium, calcium,

potassium, and sodium• What are the 3 types of magma?

– Basaltic – 50 % SiO2

– Andesitic – 60% SiO2

– Rhyolitic - 70% SiO2

• What affects magma characteristics?– Silica - SiO2

List and describe the 4 factors that List and describe the 4 factors that affect magma formationaffect magma formation

Temperature

Pressure

Water content

Mineral composition

Temperature increases with depth in crust (geothermal gradient)

Pressure increases with depth in crust due to overlying rock. As pressure increases, so does the melting pointAs water content increases, the melting point of a rock decreases

Different minerals have different melting points

DefinitionsDefinitions• Partial melting

– Not all parts of a rock melt at the same time because different minerals have different melting points

• Fractional crystallization – Different minerals form at different

temperatures as a rock cools (opposite order that they melt in)

• Layered Intrusions – Minerals form into distinct bands in the order

shown in Bowen’s reaction series

Bowen’s reaction seriesBowen’s reaction series

• Illustrates the relationship between cooling magma and crystal formation.– First pattern

• Characterized by a continuous gradual change of mineral composition in the feldspar group

– Second pattern • Characterized by an abrupt change of mineral type

in the iron-magnesium groups