Igneous Rocks How do Igneous rocks form? The answers are found in your: Text book on page 112 or Reference tables page 6 Write the answer in your notes. Then write what you see on the slides for notes.

Intrusive Vs. Extrusive <--Forms from--> <-- Crystal size--> <-- Alternate name--> <-- Texture--> Home Back

<-- Composition --> Felsic Vs Mafic <-- Color --> <-- Density --> <-- Composition --> Home Back

4 Factors that affect the formation of Magma 1. Temperature 2. Pressure 3. Water content 4. Mineral composition Home Back

1. Temperature The temperature needs to be between 800 to 1200 degrees Celsius before they melt. -Where does this heat come from in nature? Geothermal gradient: The deeper into the Earth’s crust you go, the higher the temperature gets. Home Back T e m p H L Depth increasing -->

2. Pressure Like the geothermal gradient Pressure increases with depth due to the overlying rocks Home Back P r e s H L Depth increasing -->

3. Water content The amount of water will determine the melting point of the rocks. As the water content increases the melting point decreases. Home Back W a t e r H L

4. Mineral content Different minerals have different melting points Mafic (rich with iron) rocks have a higher melting point than Felsic (Al rich) rocks Home Back

Partial melting Because not all minerals have the same melting points, not all parts of a rock melt at the same time. -Text book page 102 Home Back

Fractional Crystallization The process by which different minerals are created at different temperatures. Home Back

Bowen’s Reaction series This illustrates the relationship between cooling magma and mineral formation. There are 2 main branches 1. Feldspars 2. Iron rich minerals page 103 in text Home Back

Igneous rock chart. Found in text book page 107 Found in the ESRT’s page 6 The environment of formation is found on the left side of the chart. This corresponds to the texture on the right side. The deeper in the ground a rock forms, the slower it cools and the bigger the crystal (grain size) is. Intrusive --> coarse grained Extrusive --> glassy and or fine grained

-The further down on the chart you go, the rougher the rock is How do you use the chart? -The further down on the chart you go, the rougher the rock is -The further to the right you go, the more dense, dark and mafic it is -The further to the left you go, the less dense, lighter and felsic it is -If you forget, look at the arrows underneath the main chart on pg 6

How can you determine mineral composition? 1. Pretend that the top igneous chart is made of clear plastic. 2. Visualize that you are sliding the top chart over the bottom one. 3. What are the three minerals that Rhyolite (Middle left side) looks like it is made of? Potassium Feldspar and Quartz! Home Back

Grain size The faster the cooling rate the smaller the crystals. The slower the cooling rate the larger the crystals. Be able to show this by drawing a graph. The bigger the crystal size the rougher the texture. Home Back

IGNEOUS: ROCKS THAT FORM FROM THE SOLIDIFICATION OF MAGMA Vocabulary IGNEOUS: ROCKS THAT FORM FROM THE SOLIDIFICATION OF MAGMA INTRUSIVE: A ROCK THAT FORMS WITHIN EARTHS CRUST COOLING SLOWLY and forms LARGER CRYSTALS EXTRUSIVE: ROCKS THAT FORM ABOVE EARTHS SURFACE, COOL QUICKLY and forms SMALLER CRYSTALS FELSIC: HAS HIGH SILICA CONTENT, LIGHT IN COLOR, LOW IN DENSITY AND HAS ALUMINUM and silicon IN ITS COMPOSITION MAFIC: LOW SILICA CONTENT, DARK IN COLOR, HIGH IN DENSITY, HAS IRON AND MAGNESIUM LAVA: MAGMA THAT IS ON EARTH’S SURFACE MAGMA: MOLTEN ROCK BENEATH EARTHS SURFACE TEXTURE: HOW IT FEELS BASED ON ITS GRAIN SIZE PORPHYRY: A ROCK WITH 2 DIFFERENT TEXTURES DUE TO TWO DIFFERENT COOLING RATES. Home Back

Ch 5 Quiz 1. What is the color, composition and density of a mafic rock? 2. What are the 4 Factors that affect the formation of Magma? 3. Define Geothermal Gradient 4. What is the relationship between the cooling rate and the grain (crystal) size?

List the minerals that are found in Obsidian