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 (SiO 2 ) 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

Fissure Flood Basalts produced the Colombia Plateau

Volcano outpouring 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

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 National Park From yahoo images

Plutons