What are igneous rocks?All rocks on Earth were initially igneous. Igneous rocks form as liquid magma cools, forming crystal structured rocks. There are many different types of igneous rocks. Ignis means fire (ignite, ignition)

Where do they form?

Either deep within Earth or on Earth’s surface.

http://library.thinkquest.org/05aug/00461/igneous.htm

Two Types of Igneous Rocks

• Scientists divide igneous rocks into two different categories.

• Those which were cooled below the surface are called intrusive rocks

• Those which cooled on the surface are referred to as extrusive rocks.

Igneous Rocks- Word Connections

Extrusive- Exit, Exoskeleton,exterior

Intrusive-inside, intrude,interior

Coarse- roughFine - smooth

Intrusive/Inside • most common -intrusive igneous

rocks. • forms when a pocket of magma

slowly cools down • Turns into solid rock beneath

earth’s surface • Coarse/large grain crystals • You can see the crystals

Granite(Intrusive)

Coarse Grained Crystals

If you look closely at a piece of granite you will see little flecks of white, black, gray, and sometimes pink. These flecks of color are crystals

Intrusive

Extrusive

• Igneous rock formed from lava that has flowed out onto the Earth’s surface.

• Solidifies fast• Cools rapidly• Small/fine grains• Ex-basalt/obsidian• Can’t see the crystals

• http://library.thinkquest.org/J002289/rocks.html

Extrusive

Obsidian(Volcanic Glass)

Name of Rock Basalt Granite

Type of Igneous extrusive intrusive

Texture Glassy or fine Course,rough

Crystals Small crystals Large Crystals

Careers in Science

• Petraologists study igneous rocks• Field observations• Laboratory studies• Geochemical analyses and experiments