1. Rocks ~Igneous Rocks form from molten rock~

2. Vocabulary Magma Lava Molten rock beneath Earth’s surface
Molten rock that reaches Earth’s surface through a volcano

3. Igneous Rocks…
Formation
Cooling
Time
Crystal
Size
Mineral
Composition
Color
Origin
Igneous Rocks are classified on the basis of mineral composition and size of mineral crystals.

4. Origin of Igneous Rocks
Igneous rocks are classified as INTRUSIVE or EXTRUSIVE
Intrusive
Forms when magma cools within Earth
Magma cools slowly being exposed to high temperatures
Reach surface when forces inside Earth push rocks up & wind and water break apart/carry away surface rocks
Extrusive
Forms when lava cools on Earth’s surface
Lava cools quickly being exposed to cool temperatures
Reach surface through volcanoes

5. Intrusive Igneous Rocks
Forms from magma within Earth’s surface
Granite
Diorite
Gabbro
Peridotite
Anorthosite
Pegmatite

6. Extrusive Igneous Rocks
Forms from lava on Earth’s surface
Basalt
Pumice
Obsidian
Rhyolite
Andesite
Scoria

7. Textures of Igneous Rocks
Texture of an igneous rock is determined by the size of its
mineral crystal
Size of mineral crystals depends on how quickly the magma or lava cools.

8. Textures of Igneous Rocks
Intrusive
Interior of Earth is HOT
High Temperatures allow magma to cool SLOWLY
Slow cooling allows time for LARGE mineral crystals to form
Extrusive
Surface of Earth is COOL
Lower temperatures cause the lava to cool QUICKLY
No time for large mineral crystals to form so there are SMALL mineral crystals

9. Composition of Igneous Rocks
Texture is not enough to identify an Igneous Rock. Some Igneous Rocks have similar textures. Composition is based on Silicate levels.
Silica
Compound made up of silicon and oxygen which geologists use to classify rocks
Estimate SILICATE level by COLOR
HIGH LEVELS OF SILICA LIGHT COLOR
LOW LEVELS OF SILICA DARK COLOR
Granite/Rhyolite
Gabbro/Basalt

10. Rocks in the World Around Us

11. Rocks in the World Around Us