1. Bellringer
What are five characteristics that make up the definition of a mineral?
Quiz Wednesday: Chem – Rock Cycle
inorganic
Natural
solid
Set chemical composition
Crystalline structure

2. Igneous Rocks

3. Granite (rock made of quartz and feldspar)
Rocks
Rocks – combinations of minerals
Rocks are identified by the minerals that make them up
Granite (rock made of quartz and feldspar)
 Quartz (mineral)
Feldspar
(mineral) 

4. Rocks Three main types of rocks, all formed different ways Igneous
Sedimentary
Metamorphic

5. Igneous Rocks
Igneous rocks – rocks created from the cooling and crystallization of magma or lava
Igneous is Latin for “fire” (same root as “ignite”)
The most common rocks in Earth’s crust
Two main types

6. Types of Igneous Rocks
Intrusive rocks – form from magma that has cooled and crystallized slowly underground
Gradual cooling = rocks with larger mineral crystals
Intrusive rocks because form INside the Earth
Granite—most common intrusive igneous rock (makes up most of the continental crust)

7. Types of Igneous Rocks
Extrusive rocks – form from the rapid cooling and crystallization of lava on Earth’s surface
Rapid cooling = no or only small mineral crystals
Extrusive rocks form after they EXit Earth’s surface

8. Extrusive Igneous Rocks Intrusive Igneous Rocks
Obsidian (volcanic glass)
Rhyolite

9. Types of Igneous Rocks magma lava slowly quickly large small
Type of Rock
Intrusive Rocks
Extrusive Rocks
Form from…
Cool…
Form _____ grains/crystals
magma
lava
slowly
quickly
large
small

10. Classifying Igneous Rocks
Igneous rocks are classified two ways:
1. Mineral Composition:
Felsic – high in SiO2, low in Fe&Mg; light-colored (ex: granite)
Intermediate
Mafic: low in SiO2, high in Fe & Mg; dark-colored (ex: gabbro)
Ultramafic
granite
gabbro

11. Classifying Igneous Rocks
2. Mineral Grain Size: large grains (intrusive) or small grains (extrusive)

12. Classifying Igneous Rocks
Mineral grain shapes can be observed by looking at very thin sections under microscopes
Many mineral grains have interlocking edges that form as the grains crystallize together
Well-shaped crystal grains form during fractional crystallization by floating to the top and having space to grow
Thin section of gabbro

13. Classifying Igneous Rocks
Porphyritic texture – igneous rocks with large, well-formed crystals surrounded by finer-grained minerals
Indicates a complex cooling history where slowly-cooling magma suddenly began rapidly cooling because it erupted onto Earth’s surface

14. Uses for Igneous Rocks Building Materials
High strength due to interlocking grains
Many of the minerals are resistant to weathering
Beauty of crystals desired in modern decorating (ex: granite countertops)

15. Uses for Igneous Rocks Ore Deposits
Veins – many valuable metals (gold, silver, lead, copper) are left over at the end of magma crystallization, fill cracks in surrounding rocks, and eventually crystallize to form veins
A gold vein

16. Igneous Rock Lab Get in groups of 2-3
You will need a lab sheet (one per group), laminated directions, and a bag of rocks
IGNORE THE SAMPLE NUMBERS
Turn in paper when done and return supplies

18. Work with the same group you did on Friday. Finish your mineral lab
Work with the same group you did on Friday. Finish your mineral lab. Follow the numbers in the grid, not on the minerals.
When done, begin Igneous Rock Lab. Supplies (Lab paper, Laminated directions, bag of rocks) are by the mineral boxes. IGNORE THE SAMPLE NUMBERS. Turn in paper when done and return supplies.