Notes 5 – Igneous Rocks

Mrs. GordonEarth Science

Tuesday, April 18, 2023

1. Igneous Rocks• A. Forms when molten material

cools and hardens.

2. LocationA. Extrusive - formed

from lava on Earth's surface, cools quickly

• Examples: Basalt (dark colored, Snake River Plain, ocean floors)

• B. Intrusive - formed from magma below Earth's surface, cools slowly• Examples: Granite (light/dark

color, Rocky Mountains, Sawtooth Mts.)

3. Texture• A. Fine grained -

fast cooling = tiny crystals (basalt)

• B. Coarse grained - slow cooling = large crystals (granite)

• C. Porphyritic - TWO textures, due to slow cooling first then fast cooling• Magma is underground then an

ERUPTION occurs or simply movement closer to the surface

Other Textures:• Vesicular –

spongy, many small holes or pores = pumice

• Glassy – no grains, smooth feel, sharp edges = obsidian

•4. Mineral Composition• A. High SILICA (quartz) = light color

• B. Low SILICA (quartz) =dark color

5. USES• A. BasaltA. Basalt - crushed to make roads• B. Obsidian - sharp tools• C. Granite - building materials• D. Pumice - cleaning materials, face wash