Download I. Composition of the Earth`s Crust

I. Composition of the Earth’s Crust
A.  The earth’s crust is composed of rocks.
• 
A rock is defined as two or more minerals, found in the
earth’s crust bonded together in a solid form
B.  98% of the earth’s crust is composed of the following 8
elements:
• 
Silicon (Si), Oxygen (O2), Aluminum (Al), Magnesium
(Mg), Calcium (Ca), Sodium (Na), Potassium (K) and
Iron (Fe)
II. Rock Types
A.  Sedimentary rocks - • 
formed by the hardening and cementing of layers of
sediment.
B.  Metamorphic rocks - • 
formed when rocks that already exist are changed by
heat and pressure into new kinds of rocks.
C.  Igneous rocks - • 
formed by cooling and hardening of hot molten rock
from inside the Earth. III. The Rock Cycle
IV. Studying Igneous Rocks
A.  Color: • 
Indicates differences in chemical composition. B.  Crystal size: (mm)
• 
Indicates the rate of cooling of a rock.
• 
Rocks with larger crystals cooled more slowly than rocks
with smaller crystals. C. Density: mass (g) ÷ volume (ml or cm3)
• 
Indicates differences in depth of formation and chemical
composition. • 
More dense rocks form from magma that originates deeper
in the mantle.
V. Igneous Rock Formation
A. Three major factors affect the chemical composition, crystal
size and density of Igneous Rock:
1.  Source of parent magma. 2.  Interaction between the parent magma and the rocks of
the crust.
3.  Rate of cooling.
VI. Types of Igneous Rocks
A.  Intrusive Igneous Rock • 
Definition: rock formed underground when magma cools.
• 
Magma: molten (liquid) rock found beneath the earth’s
surface.
1. Cooled very slowly
Deep
Large Crystals
B. Extrusive Igneous Rock • 
Definition: rock formed on the surface when lava cools.
• 
Lava: molten (liquid) rock that emerges from the crust
through cracks or fissures.
2. Cooled very quickly
Surface
Fine Crystals/
Glassy Rock
VII. Igneous Rock Characteristics
A. Felsic Rocks
• 
Chemical Composition: High percent of silicates (Si) and water.
Low percent of iron (Fe), calcium (Ca), & magnesium (Mg)
• 
Color: Light colored minerals
• 
Viscosity: The degree to which a substance resists flow. • 
Relative Level: High (Low temperatures and slow flowing)
• 
Trapped gases: High level: H2O, O2, CO2, H2, CO, H2S, SO2
• 
Relative Density Level: Low (high gas content)
• 
Volcanic source: Explosive volcanoes and
cinder cones (ex. Mt. Pinatubo)
• 
Location: Continental Crust
B. Mafic Rocks
• 
Chemical Compostion: Low percent of silicates (Si). High in Calcium
(Ca), Iron (Fe) and Magnesium (Mg). • 
Color: Dark colored minerals
• 
Relative Viscosity Level: Low (high temperature and more fluid)
• 
Trapped gases: Low level
• 
Relative Density Level: High (low gas content)
• 
Volcanic source: “Gentle” eruptions from broad
volcanoes (ex. Hawaii)
• 
Location: Oceanic Crust and Hot Spots
shield
C. Andesitic (Intermediate) Rocks
• 
Chemical Composition: Intermediate percent of silicates (Si).
Intermediate in Ca, Fe, Mg. • 
Color: Intermediate colored minerals
• 
Relative Viscosity Level: Intermediate
• 
Trapped gases: Intermediate amounts present
• 
Relative Density Level: Intermediate
• 
Volcanic source: Intermediate eruption volcanoes
• 
Location: Continental Crust
VIII. Review
A.
[ Si]
[Ca, Fe, Mg]
[ Si]
Felsic
Mostly light
colored minerals
B. Mafic
Mostly dark
colored minerals
C.
[Ca, Fe, Mg] Andesitic
Contain light and dark minerals
Intermediate levels of [Si, Ca, Fe, Mg]
A. Felsic
!
!
Dissolved
Gases
Thick & Slow
B. Mafic
! !
!Dissolved
! Gases!
!Thin & Fast!
!
Hard For Gases
! To Escape
!Gases Escape!
! ! Easily!
!
Explosive Eruptions
“Gentle” Eruptions
Note: Dissolved Gases Include H2O, S, CO2, H2, CO, H2S, SO2
IX. Summary
Lighter
colored
rocks
Darker
colored
rocks
Large
crystals
Small
crystals
No
crystals
Intrusive
Extrusive
Felsic
Fine
crystals
Andesitic
Small
crystals
Large
crystals
Mafic
X. Plate Tectonics and Igneous Rocks