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Physical Science
Igneous Rocks
Three Rock Types
• Igneous – formed by molten magma
• Sedimentary – formed from deposited material
• Metamorphic – formed as rock is subjected to heat and pressure
From yahoo images
Igneous Rocks
• Make up 95% of earths crust
• Most common are on the continents - Andesite and Granite
• Most common on the ocean floor – basalt
• All Igneous rocks originate as magma or molten rock from the earths interior
From yahoo images
Igneous Rocks
• Rocks start melting at 750 C
• Temp increases about 30 °C each km toward the center of the earth
Igneous Rocks
Melting depends on pressure & water content
Higher pressure – higher melting point More water – lower melting point
Rocks with lower melting point will melt first and solidify (crystallize)
first when cooled
Magma is classified by the amount of silica (SiO2) that it contains
Basaltic – 50% silica
Andesitic – 60% silica
Granite – 70% silica
Igneous Rocks
• Extrusive – Rocks that form at the earths surface (lava)
• Intrusive – Rocks that form beneath the earths surface
From yahoo images
Extrusive
Lava – molten material from the earth and the rocks that form from it
Fissure – outpouring of basaltic lava on the ocean floor
Volcano – outpouring of lava through a vent
From yahoo images
FissureFlood Basalts produced the Colombia Plateau
Volcanooutpouring of lava through a vent
Shield volcano – broad gentile slopes
Cinder cone – smooth steep slopes and a bowl shaped summit
Composite cones – steep sided summit – gradual slopes
From yahoo images
Volcano
Intrusive Rock
• Rock Formations that occur under ground by molten magma called plutons
• Plutons – large intrusive rock body beneath the earths surface including dike, batholith, laccolith, sill,
Plutons
Plutons
• Dike – formed by the intrusion of magma into fractures
that cut across the layers of existing rock
• Shiprock – New Mexico
From yahoo images
Plutons
• Sill – intrusion of magma into fractures that are parallel to the layering
From yahoo images
Plutons
• Laccolith – mushroom shaped sill that pushes the rock layers upward
From yahoo images
Plutons
• Batholiths – large sill or laccolith having a surface area greater than 100 square kilometers – usually due to a number of intrusive events
From yahoo images
Batholiths
Yosemite NationalPark
From yahoo images
Plutons