1. Igneous Rocks
“Liquid Hot Magma!”

2. Igneous Rocks Rocks formed from cooling of lava or magma
Lava-Melted rock erupted from volcanoes and deposited on the earth’s surface. Cools quickly.
Magma-Melted rock that sits inside the earth in a magma chamber. Cools slowly.
Magma Chamber

3. Types of Igneous Rocks 2 major types: Intrusive and Extrusive
Intrusive igneous rocks cool and harden inside the earth.
Extrusive igneous rocks cool and harden on the earth’s surface or outside the earth.

4. Intrusive Igneous Rocks
Form when magma cools before reaching the surface.
Cool very slowly
Intrusive igneous rocks have large, interlocking crystals because they cooled slowly inside the earth.
Examples are Granite, Gabbro, Diorite, and Unakite (Virginia’s State Rock!)
Granite
Unakite

5. Extrusive Igneous Rocks
Form when lava erupts and hardens on the surface.
Cool very quickly
Extrusive igneous rocks have fine (small) to no crystal grains at all.
A rock with no visible grains is called a volcanic glass (examples are pumice and obsidian).
Examples are Obsidian, Pumice, Scoria, Basalt, Tuff, Porphyry (cools inside then erupts), Rhyolite, Andesite.
Rhyolite
Obsidian

6. Texture of Igneous Rocks
Grain Size (Glassy, Fine, Medium, Coarse)
Grain Shape (Irregular, Angular)
Sorting:
Glassy: Looks like glass (Obsidian, Pumice)
Aphanitic: Can’t see crystals (Scoria, Tuff)
Porphyritic: Large crystals in fine matrix (Porphyry)
Phaneritic: Medium to Large interlocking crystals (Granite, Diorite, Gabbro)

7. Textures
Glassy
Phaneritic
Aphanitic
Porphyritic

8. Vesicles Vesicles are holes found ONLY in Igneous rocks.
Formed from trapped gasses when lava erupts
Examples: Scoria, Pumice, Basalt (sometimes)

9. Tectonic Plate Boundaries
Places where tectonic plates converge, diverge, or slip past each other.

10. Igneous Rocks form at Convergent Boundaries
Ocean-Continent Convergent Boundary.
Forms volcanoes like those in Washington State.

11. Igneous Rocks form at Divergent Boundaries
Divergent Boundary or Spreading Ridge
Forms volcanoes like those that make up Iceland and the mid-Atlantic Ridge.

12. Mid-Atlantic Ridge

13. Igneous Rocks Form at Hot Spots
A hot spot is where magma rises to the surface in the middle of a plate and not a plate boundary.
Forms volcanoes like those in Hawaii or Yellowstone.

14. Hot Spots
Hawaii
Yellowstone