What is a What is a Rock?Rock?

•A rock is a:A rock is a:–Naturally formed,Naturally formed,–Consolidated material,Consolidated material,–Composed of grains of Composed of grains of one or more minerals.one or more minerals.

Some RocksSome Rocks

Types of Common Types of Common RocksRocks

•There are three types There are three types of common rocks:of common rocks:–Igneous rockIgneous rock–Sedimentary rockSedimentary rock–Metamorphic rockMetamorphic rock

Igneous RockIgneous Rock

•Igneous rocksIgneous rocks form form from the solidification from the solidification of magma.of magma.–ExEx: pumice, obsidian: pumice, obsidian

Identifying Identifying IgneousIgneous RocksRocks

• Where the igneous rockigneous rock forms in the crust shapes their composition so igneous rocks are identified by their texture.– Extrusive rocksExtrusive rocks form at or near the surface and are fine-fine-grained.grained.

– Intrusive rocksIntrusive rocks form below the surface and are coarse-coarse-grainedgrained.

Basalt: Basalt: IgneousIgneous – – ExtrusiveExtrusive, Fine-, Fine-

grainedgrained

Granite: Granite: IgneousIgneous – – IntrusiveIntrusive, Coarse-grained, Coarse-grained

Igneous Rock Features:Igneous Rock Features: FelsicFelsic

• Felsic rocksFelsic rocks are rich in potassium feldspar and quartz and are light in colorlight in color. – Example is the granitegranite family of

rocks.

• Felsic rocksFelsic rocks are most common in the continentscontinents.

Felsic Igneous RocksFelsic Igneous Rocks

Igneous Rock Features:Igneous Rock Features: MaficMafic

• Mafic rocksMafic rocks are rich in darkdark plagioclase feldspar and pyroxene.– Example the gabbrogabbro family of

rocks.

• Mafic rocksMafic rocks are more common in the ocean basinsocean basins.

MaficMafic Igneous Rocks Igneous Rocks

Basalt

IgneousIgneous IdentificationIdentification

• Some igneous rocks have holes Some igneous rocks have holes in them that formed during the in them that formed during the cooling of the magma. These cooling of the magma. These types are said to betypes are said to be vesicularvesicular.

Igneous RocksIgneous Rocks

Structure of Structure of IgneousIgneous RocksRocks

• ShieldShield and Cinder ConeCinder Cone volcanoes will erupt and create lava flows, and lava plateauslava plateaus, that form igneous rocks.

• When magma does not erupt but instead forces its way up through cracks and faults it produces large masses of intrusive rock called plutonsplutons.

Shield (Etna) and Cinder Cone Shield (Etna) and Cinder Cone (Paracutin)(Paracutin)

PlutonsPlutons• PlutonsPlutons are classified according to size:• SillsSills are slabs of igneous rock parallel

to the rocks they intrude;• DikesDikes are slabs of igneous rock that cut

across the rock layers they intrude;• A laccollithlaccollith forms between two rock

layers, bulging up to form a dome;• A batholithbatholith is the largest intrusion and

they form the core of many mountain ranges.

• When a volcano erodes the harder volcanic neckvolcanic neck is often left behind.

Devil’s Tower is the result of igneous rock that was underground until all the weaker surrounding rock was eroded