Chapter 6 2 IGNEOUS ROCKS Igneous Rock When
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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
