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

Mineral -Naturally formed-Solid-Formed by inorganic processes-Specific chemical composition-Characteristic crystal structure

Earth Materials continued

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

SedimentaryRocks

IgneousRocks

MetamorphicRocks

Magma

Sediment

Pressure

And Cementation

Erosion

Erosion

Heat and Pressure

CoolingHeat

Heat

Pressure Ero

sion

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

Factors controlling Melting2. Pressure:• as pressure increases, melting

temperature increases• as pressure decreases, melting

temperature decreases

Lowering pressure causes melting in divergent margins.

Divergent Plate Boundary

Relationship between P, T, and Melt

Factors controlling Melting

3. Water content:as water content increases, melting temperature decreases

Water in rocks causes melting in convergent margins.

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 flowhoney – high viscositywater – 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 content75% SiO2 - "high" silica content

Endmember Magma Chemistry

Mafic – low SiO2, iron, magnesium

Felsic/Silicic – high SiO2, 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.

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

Textures of Igneous Rocks

Phaneritic (course grained)

Aphanitic (fine grained)

1.

2.

3.

4.

Glassy

Vesicular

Magma

Lava

Felsic/ Silicic Mafic

light colored intermediate dark colored

high in SiO2 low in SiO2

Phaneritic Plutonic (magma)

(coarse grained) Intrusive

Aphanitic Volcanic (lava)

(fine grained) Extrusive

Igneous Rock Classification

Granite

Rhyolite

Diorite Gabbro

Andesite Basalt

Increasing Fe and Mg

Increasing silica content

Aphanitic Texture – Rapid Cooling Small Crystals

Phaneritic Texture – Slow Cooling Large Crystals

Phaneritic Texture –Slow Cooling

Large Crystals

Aphanitic Texture –Rapid CoolingSmall Crystals

Silicic Chemical Composition

Granite Rhyolite

Phaneritic Texture –Slow Cooling

Large Crystals

Aphanitic Texture –Rapid CoolingSmall Crystals

Intermediate Chemical Composition

Diorite Andesite

Phaneritic Texture –Slow Cooling

Large Crystals

Aphanitic Texture –Rapid CoolingSmall Crystals

Mafic Chemical Composition

Gabbro Basalt

Phaneritic

Porphyritic-Phaneritic

Phenocrysts in Groundmass

Aphanitic

Porphyritic-Aphanitic

Phenocrysts in Groundmass

Pegmatites

Ingersoll Mine Ingersoll mine, Pennington Co., South Dakota, United StatesOne of the many adits at the old Ingersoll pegmatite. Private and Very dangerous. No Trespass.

Glassy Texture - Very Rapid Cooling - No Crystal Structure

Ash Fall Ash Flow

Pyroclastic Texture

Plutonic Structures

Plutonic Structures