1. 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

3. L Igneous formed from Magma and Lava Magma • molten rock below Earth's
surface. L
ava •
magma on the Earth's surface.
Pyroclastic material • (
pyro
= fire,
clastic
= debris) •
Airborne lava —
cools as it falls

4. Composition of the magma•
Analogous to what makes up the “stew" •
What chemical elements are present •
What material has the magma moved
through
Temperature of the melt •
Not only how hot, but how long it stays that hot •
also relates to pressure of the molten rock
Cooling environment •
fast vs
slow •
Internal vs External
Water content

5. Bowen's Reaction Series-
IMPORTANT!
Plagioclase
Olivine
(Ca-feldspar)
Pyroxene
Continuous
Discontinuous
Amphibole
Plagioclase
Biotite
(Na-feldspar)
Orthoclase
(K-feldspar)
Muscovite
Quartz

6. What things might you describe when looking at an igneous rock?

7. between the two extremes in Si content and other atoms. Mafic magma •
Composition of Igneous rocks
Felsic or Sialic
magma •
Si-rich (> 65%) •
rich in K, and Al •
little Ca, Fe, and Mg.
Intermediate magma •
between the two extremes in Si
content and other atoms.
Mafic
magma •
Si - poor (< 35%)
richer in Ca, Fe, and Mg. •

8. Ways of Changing Magma Composition

9. Viscosity of Magma/ Lava Viscosity of Magma/ Lava
Viscosity- important for volcanic activity • •
the resistance of a liquid to flow
the resistance of a liquid to flow — —
high viscosity = thick and stiff — —
low viscosity = thin and "runny".
Related to:
Related to: • •
amount of water (H2O) in magma • •
amount of silica (Si) in magma • •
Mafic
Mafic — —
thin, low viscosity • •
Felsic
Felsic — —
thick, high viscosity

10. Igneous Rock Textures- how big are the Phaneritic Texture
minerals?
Phaneritic Texture •
Visible Mineral Grains
distinguishable as different colored interlocking
shapes
Aphanitic Texture
Mineral grains too small to be seen —
microscopic
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

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

12. Cooling Histories Minerals need time and space to grow•
More time = Bigger crystals —
visible mineral grains
P & T control cooling rates of magma
Temp
Earth is a good insulator
holds in heat
keeps out cool
Atmosphere is a relatively bad insulator
transfers heat easily
Earth has pressure
Weight of overlying rocks
Magma trying to push up (density)
water vapor (steam), wants to expand

13. Categories of Igneous EOF
Granite
Intrusive rocks •
cool beneath Earth's surface •
cool very slowly •
higher P & T —
Phaneritic textures
Rhyolite
Extrusive rocks •
cool on the Earth's Surface •
cool relatively fast •
lower T & P —
Aphanitic textures
Basalt porphyry —
Pyroclastic textures
Complex •
Partially cools below and above —
Porphyritic textures

14. Igneous rock names • determined by texture •—
size and arrangement of mineral grains •
AND by mineral composition —
minerals affect rock color and indicate temperature of creation

15. 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

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

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

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

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

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

21. Tuffs & Breccias- look like sedimentary rock Tuffs & Breccias
But they are not….it is volcanic ash that is lithified

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

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

24. Sierra Nevada Batholith- Home to Yosemite National Park and a lot of Granites and Grano-diorites

25. Sierra Nevada Batholith

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

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

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

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