1. IGNEOUS ROCKS

2. Rocks are divided into 3 categories
The Rock Cycle-
Minerals form rocks
All rocks can be transformed into other rock types
Rocks are divided into 3 categories
Igneous- crystalline- forms as liquid cools
Metamorphic- crystalline-forms as rocks are heated and squeezed
Sedimentary- non-crystalline- smaller pieces or chemicals from other rocks

4. Igneous Rocks Formed From Magma and Lava
Magma - molten rock below Earth's surface.
Lava magma on the Earth’s surface.
Pyroclastic material (pyro = fire clastic = debris
Airborne Lava - cools as it falls.

5. What terms might you use to describe when looking at an igneous rock?

6. Igneous Rock Textures

7. Viscosity of Magma/ Lava
Viscosity is important for volcanic activity.
It is the resistance of a liquid to flow
High viscosity is thick and stiff
Low viscosity is thin and “runny”
Is determined by the amount of:
Water in the magma
Amount of silica in the magma
Mafic is thin and has low viscosity
Felsic is thick and has high viscosity. •

8. Phaneritic Texture
Visible Mineral Grains
distinguishable as different colored interlocking
shapes
Aphanitic Texture
Mineral grains too small to be seen
microscopic

9. Igneous Rock Textures- how big are the minerals?
Porphyritic Texture
Two distinct sizes of mineral grains
Large and Small
Large = Phenocrysts
Small = Groundmass or Matrix
Groundmass
Grains may be either visible or not

10. Porphyritic texture
Aphanitic basalt (mafic composition) constitutes the groundmass

11. Categories of Igneous EOF
Granite
Intrusive rocks
cool beneath Earth's surface
cool very slowly —
Phaneritic textures
Extrusive rocks
Rhyolite
cool on the Earth's Surface
cool relatively fast
Aphanitic textures
Basalt porphyry
Complex
Partially cools below and above
Porphyritic textures

12. Pegmatite A Pegmatite is a very coarse-grained igneous rock.
Crystals are >2 cm, often larger.
Most are granitic, although mafic pegmatites can form.
Biotite mineral
grain
Feldspar
mineral
grain
Quartz mineral
grain

13. Granite & Rhyolite Felsic magma Phaneritic Texture Granite
What are the textures in these two rocks ?
Aphanitic Texture

14. Andesite & Diorite Phaneritic texture Aphanitic texture
-forms from intermediate
composition magma
Aphanitic texture
forms from intermediate
composition magma
What are the textures in these two rocks ?

15. Basalt & Gabbro Gabbro Basalt aphanitic texture phaneritic texture
forms from mafic magma
phaneritic texture
forms from mafic magma

16. Peridotite- the abundance of Olivine crystals (more than 40%) makes the rock take on a green appearance

17. Obsidian- a popular rock among paleopeople for tool making
Volcanic
Glass

18. How do we tell where the igneous rocks formed and what can we derive from the rocks about the conditions of formation?

19. Pyroclastics
Lava flow
Volcanic neck
Igneous dike
Igneous Sill
Batholith

22. A batholith is a large mass of intrusive igneous rock, larger than 100 square miles in area, that forms from cooled magma deep in the Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock types, such as granite, quartz monzonite, or diorite.

23. Sierra Nevada Batholith- Home to Yosemite National Park and a lot of Granites

24. Sierra Nevada Batholith

26. Areal extent of the Idaho Batholith- a huge (15,400 square miles) intrusive body of primarily felsic composition (granites) igneous rocks

27. Discordant with surrounding rock It cuts across other rocks
An igneous dike-
Discordant with surrounding rock
It cuts across other rocks

28. Concordant with surrounding rock It runs parallel to other rocks
An igneous sill-
Concordant with surrounding rock
It runs parallel to other rocks

29. Necks & Ig Dikes
Neck
Dike
igneous sill
Igneous sill