1. Warm-Up: Fri 4/11 Write What You Know!
Write everything you know about the prompt below for five minutes, try for at least 3-4 complete sentences.
Describe the three major classes of rocks based on how the rocks form.

2. 4/11/2014 Igneous Notes Major Key Term Key Term
definition in own words
Key Term
definition in own words
facts
pictures
Key Term

3. Igneous Rocks
Igneous – comes from the Latin “ignis” which means “fire” rocks from fire!
Igneous rocks are rocks formed by the cooling and hardening of magma and lava
Igneous rocks are classified according to origin, texture, and composition

4. Origin
Intrusive Rocks: form underground from magma, tend to have larger crystals (coarse-grained)
Extrusive Rocks: form on the surface from lava, tends to have smaller crystals (fine-grained)

5. Texture
Minerals crystallize, form crystals, as solutions of magma/lava cool down
The slower the magma/lava cools, the larger the crystals (coarse-grained, intrusive)
The faster the magma/lava cools, the smaller the crystals (fine-grained, extrusive)

6. Mineral Composition Silica SiO2
Darker colored rocks usually low in silica, such as basalt
Lighter rocks usually high in silica, such as granite
Silica
SiO2

7. Common Igneous Rocks
Granite: intrusive, coarse-grained, high silica – used for building materials
Basalt: extrusive, fine-grained, low silica
Pumice: extrusive, fine-grained, high silica, low density (lots of bubbles from escaping gas) – used as an abrasive
Obsidian (volcanic glass): extrusive, no grains!, low silica – used by ancient peoples to make weapons