Physical Science Igneous Rocks. Three Rock Types Igneous – formed by molten magma Sedimentary –...

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