1. Igneous Rocks
Igneous – “FIRE ROCKS”
From red-hot magma…

2. Extrusive Igneous Rocks
form when lava erupts from a volcano or “bubbles up” from tectonic plates moving apart - onto Earth’s surface.
Ex: Basalt – the most common extrusive rock on Earth; forms most of Earth’s ocean floor.
Ex: Obsidian – black volcanic glass

3. Igneous Rocks
Earth's Most Abundant Bedrock: Basalt
Basalt forms more of Earth's surface than any other rock type. Most areas in ocean basins are basalt.
May be on land from lava flows, too.

4. Igneous Rock - Obsidian
Obsidian was used to make knives, arrow heads, spear points, scrapers and many other weapons and tools

5. How igneous rocks form…
Extrusive
When a volcano erupts or when magma bubbles to the surface
Intrusive when magma cools slowly inside earth

6. Intrusive Igneous Rocks
forms when magma hardens beneath Earth’s surface (INSIDE).
Ex: Granite – the most abundant intrusive rock on Earth’s continents.
Forms the core of many mountain ranges.
Ex: Porphyry- looks like jello w/fruit inside it

7. Intrusive Igneous Rocks
Granite
is used to make many objects
Granite is also well-known from its many world-famous natural exposures.
These include: Stone Mountain, GA; Mount Rushmore, SD

8. Intrusive Igneous Rock
Porphyry—mixed texture (some large and some small grains)

9. Igneous Rocks Texture – fine grained
Rapidly cooling lava forms a fine-grained rock with small crystals.
Ex: Basalt - crystals too small to be seen without a microscope.
Ex: Obsidian –smooth, shiny texture like thick glass & cooled without forming crystals “Volcanic Glass”

10. Igneous Rocks
Obsidian
Obsidian on the side of a volcano

11. Igneous Rocks Texture: coarse-grained
Slowly cooling magma forms coarse-grained rock with large crystals
Ex: granite and porphyry

12. Igneous Rocks – Mineral Composition
Felsic: When magma is high in silica light-colored rocks form - like granite.
Mafic: When lava is low in silica dark-colored rocks form - like basalt

13. High Silica vs. Low Silica
Felsic vs. Mafic

14. Uses of Igneous Rock
Granite – Statues, Bridges and old public buildings, Paving streets with cobblestone, floors, kitchen countertops (thin polished sheets of Granite)

15. Uses of Igneous Rock Basalt - Gravel for construction
Obsidian - Sharp tools for cutting and scraping (Native Am!), Starting vegetable gardens (fertilizer) – it’s called Perlite, which is formed from heating Obsidian

16. Pumice is cool! It can float!
Pumice – used for cleaning and polishing

17. Uses of Igneous Rock
Statues, Public Buildings - Granite

18. Uses of Igneous Rocks
Cobblestone streets, kitchen countertops – Granite