Igneous Rock 12/1/14

4-2 pgs. 87-90

IN: Explain, using words and pictures, how rocks form.

sedimentary rock sediment

magmaco

oling,

crysta

llizati

on

weath

erin

g

and e

rosio

n

compaction, cementation

melting

hig

h t

em

pera

ture

gre

at

pre

ssure

igneous rock

metamorphic rock

How are igneous rock formed?Rocks are heated enough to melt its minerals into magma.

Magma cools into various types of igneous rock depending on the composition of the magma and the amount of time it takes the magma to cool and solidify.

How are igneous rock classified?Like all other rock, igneous rock is classified according to its composition and texture.

How does magma form?Temperature

An increase in temperature deep within the Earth’s crust can cause the minerals in a rock to melt.Different minerals melt at different

temperatures, from about 700 to 1250 degrees Celsius.

How does magma form?Pressure

The high pressure deep within the earth forces minerals to stay in the solid state, so when hot rocks rise to shallow depths the pressure is released and they melt.

How does magma form?Composition

Sometimes fluids like water and carbon dioxide enter a rock that is close to its melting point.

Remember, water melts above 0 degrees Celsius and carbon dioxide melts above -78 degrees Celsius.

CompositionFelsic - light-colored (Light as a Feather)Less dense…lightRich in elements such as silicon, aluminum, sodium and potassium.

Granite, Obsidian,Pumice

CompositionMafic - dark-colored (dark as Midnight)More dense…heavyRich in elements such as iron, magnesium, and calcium

Basalt

TextureIntrusive Igneous Rock

When magma cools beneath the Earth’s surface.Coarse-grained textureCools slowly

Granite & Basalt (becausethe pressure of the oceanmakes the crystals small)

Big amount of time=Big crystals=Coarse Grain

TextureExtrusive Igneous Rock

When lava cools on the Earth’s surface.Fine-grained textureCools quicklySmall

amount of time=small crystals Pumice & Obsidian

GraniteIgneous plutonic rock formed when

magma cools slowly.Remember it’s made up of mica,

feldspar, and quartz...all silicates.FelsicIntrusiveCoarse-grained

BasaltIgneous volcanic rock with small

crystals made when lava cools.MaficIntrusive/ExtrusiveFine-grained

ObsidianIgneous rock formed from

volcanoes that has sharp edges and looks like glass.FelsicExtrusiveFine-grained

PumiceIgneous rock with holes and can

float on water.FelsicExtrusiveCoarse-grained

OUT: What are some features of igneous rocks?