Igneous Rocks

Geo Facts

• Started in 1948 and located in SD• The head is 26 m tall, his arm more than

70 m long• Made of feldspar, diorite, and quartz

• Crazy Horse video segment

What is a ROCK?• A rock is a group of

minerals bound together

• In the picture you can see hornblende, feldspar, mica, and quartz

• Rocks are found in Earth’s crust and mantle

• Rocks are classified according to how they were formed:– Igneous– Sedimentary– Metamorphic

Lava vs. Magma

• Magma is molten rock below Earth’s surface

• Lava is magma that flows out onto Earth’s surface

• Magma is often a slushy mix of rock, dissolved gases, and mineral crystals

• The common elements present in magma are the same major elements that are found in Earth’s crust:– Oxygen, silicon, aluminum, iron, magnesium,

calcium, potassium, and sodium

Composition of Magma

Magma Classification• Felsic magma – thick

and slow moving• Contains large

amounts of silica• Hardens into rocks of

light-colored minerals (quartz and feldspar)

• Mafic magma – hot, thinner and more fluid

• Contains small amounts of silica

• Hardens in to rocks of dark-colored minerals (hornblende, auguite, biotite)

Magma Classification

Volcano Lava

• NatGeo volcano lava video segment

IGNEOUS

• Rocks are formed by the cooling and hardening of hot, molten rock, or magma, from inside the Earth.

• Igneous rock is slowly broken down by weathering and erosion.

Igneous Rock Formation

• Igneous rocks are classified by their mineral composition and texture.

• Intrusive igneous rocks form from underground magma.

• Extrusive igneous rocks form at Earth’s surface.

Texture

• Refers to the size, shape, and distribution of the crystals and grains that make up a rock

• Extrusive rock – small crystal size; lava cools very quickly

• Intrusive rock – large crystal sizes; lava cools very slowly

Intrusive Rock Extrusive Rock