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Purchase lab manual in lab this week
Homework 1 due in lab this week
Homework 2 due in lab next week
Read Mt. Saint Helens disaster paper
Igneous Rocks
Earth Materials continued
Mineral -Naturally formed
-Solid
-Formed by inorganic processes
-Specific chemical composition
-Characteristic crystal structure
Rock – a coherent, naturally occurring solid,
consisting of an aggregate of one or
more minerals, or a mass of natural
glass or organic matter.
Basic Rock Classifications
•Igneous
•Sedimentary
•Metamorphic
Rock Cycle
And
Sedimentary
Rocks
Metamorphic
Rocks
Erosion/ Weathering
Heat and Pressure
Magma
Sediment
Igneous
Rocks
?
Define - Freeze
?
Igneous Rocks
-a rock that forms when hot molten rock
(magma or lava) cools and freezes solid
Two types of igneous rocks
• Plutonic – cools underground
• Volcanic – cools above ground
Factors controlling Melting
1. Temperature:
Melt at [800oC and 1200oC]
Source of heat [radioactive decay]
Geothermal Gradient – the rate at which
temperature increases with depth in the Earth
30OC/km
Bowen’s Reaction Series
The order of crystallization of the common silicate minerals from a magma
Liquid
Solid
Iron and Magnesium rich
Dark colored minerals
Al, Ca, and Sodium rich
Light colored minerals
Factors controlling Melting
2. Pressure:
•
as pressure increases, melting
temperature increases
• as pressure decreases, melting
temperature decreases
Lowering pressure causes melting in
divergent margins.
Relationship between P, T, and Melt
Less Pressure
More Pressure
Divergent Plate Boundary
Factors controlling Melting
3. Water content:
As water content increases, melting
temperature decreases
Caramel is melted sugar
Water increases melting
at convergent plate boundaries
Where do igneous rocks occur?
Types of Molten Material
1. Magma – molten material below
the Earth's surface
2. Lava – molten material above
the Earth's surface
Magma Composition Changes
•Partial melting
•Assimilation
•Magma Mixing
•Fractional Crystallization
Partial Melting
some minerals
melt at a lower
temperature
than others.
Magma Viscosity
Viscosity – resistance to flow
honey – high viscosity
water – low viscosity
Viscosity increases as silica
content increases.
Magma Chemistry
Molten material can consist of liquid
rock, mineral grains and gases
(H2O, CO2, SO2).
Silicon and oxygen (SiO2) make up
the majority of magma
45% SiO2 - "low" silica content
75% SiO2 - "high" silica content
Endmember Magma
Chemistry
Mafic – low SiO2 / high iron, magnesium
Felsic/Silicic – high SiO2 / high aluminum,
calcium, sodium
Igneous Rock Types
Intrusive (plutonic) rock – cools
and solidifies below the Earth's
surface.
Extrusive (volcanic) rock – cools
and solidifies above the Earth's
surface.
Textures of Igneous Rocks
Texture – overall appearance, related
to size, shape, and arrangement of
minerals.
Texture is related to cooling history of
an igneous rock, not its chemistry.
Textures of Igneous Rocks
1. Aphanitic (fine grained)
2. Phaneritic (course grained)
Lava
Magma
Aphanitic Texture – Rapid Cooling
Small Crystals
Phaneritic Texture – Slow Cooling Large
Crystals
Silicic Chemical Composition
Phaneritic Texture –
Slow Cooling
Large Crystals
Granite
Aphanitic Texture –
Rapid Cooling
Small Crystals
Rhyolite
Intermediate Chemical Composition
Phaneritic Texture –
Slow Cooling
Large Crystals
Diorite
Aphanitic Texture –
Rapid Cooling
Small Crystals
Andesite
Mafic Chemical Composition
Phaneritic Texture –
Slow Cooling
Large Crystals
Gabbro
Aphanitic Texture –
Rapid Cooling
Small Crystals
Basalt
PHANERITIC texture
It means that the size of all grains in the rock are large
enough to be distinguished with the unaided eye
APHANITIC texture
It means that not all grains in the rock are large enough to
be distinguished with the unaided eye. Most of the rock is
background mass.
Pegmatites
Ingersoll Mine
Ingersoll mine, Pennington Co., South
Dakota, United States
One of the many adits at the old Ingersoll
pegmatite.
Private and Very dangerous. No Trespass.
Glassy Texture - Very Rapid Cooling
- No Crystal Structure
Pyroclastic Texture
Ash Fall
Ash Flow
Plutonic Structures
Plutonic Structures