Chapter 6 2 IGNEOUS ROCKS Igneous Rock When

Chapter 6 - 2 IGNEOUS ROCKS

Igneous Rock When magma cools and hardens Most made of crystals

Magma Formation 3 factors: 1. Temperature 2. Pressure 3. Fluid in rock Melting point determined by chemical composition

Melting Water added to hot rock causes melting Decreases melting point

Partial Melting Partial melting – different minerals in rock melt at different temperatures

Fractional Crystallization Chemicals in magma combine to form minerals Each have different freezing points F. C. – crystallization and removal of different minerals during cooling

Crystals that form early are larger More time to form

Intrusive Igneous Rocks Formed from magma cooling inside the Earth More time to cool Larger crystals

Extrusive Igneous Rocks Formed from lava cooling outside of the crust Cools faster Less time for crystals to form smaller

Coarse-Grained Igneous Rocks Large mineral grains Cooled slowly Intrusive Granite

Fine-Grained Igneous Rocks Small mineral grains Very hard to see Cooled fast Extrusive Basalt

Other Textures Porphyritic texture – large and small crystals Formation? Glassy Texture – cooled fast with low dissolved gases

Vesicular texture – lots of gases trapped Fast cooling Vesicles – holes in rock

3 Families determined by mineral composition

Felsic Contains a lot of silica Light colored Granite Rhyolite Obsidian Pumice

Mafic Lower amounts of silica Irion and magnesium Darker coloring Basalt Gabbro

Intermediate amounts of silica Diorite Andesite

Batholiths Large igneous intrusion At least 100 km 2 when exposed “Deep rock” 1, 000’s of meters deep

Stocks Cover less than 100 km 2 Small intrusion

Laccoliths Magma flows between rock layers Pushed rock into a dome “Lake of rock”

Sills Magma flows between rock layers and hardens Centimeters to 100’s of meters Parallel to rock layers

Dikes Magma forces through cracks and hardens Cut across rock layers

Igneous Extrusions Form on Earth’s surface Volcano – vent for magma and gases Volcanic neck – soft parts of volcano erode away

Lava Flows Lava flows – flat masses of rock

Lava Plateau Lava flow that covers a large area of land

Tuff – ash and other solid particles released from a volcano