Igneous Rocks Intrusive and extrusive rocks formed from the cooling and crystallization of magma.

Magma vs. Lava Magma is molten rock beneath Earth’s surface Lava is magma that has flowed out onto Earth’s surface

Two types of Igneous Rocks Extrusive Igneous Rocks Fine grained igneous rocks that cool quickly on the Earth’s surface(forms from Lava). Ex. Rhyolite Intrusive Igneous Rock Course grained Igneous rock that cools slowly beneath the Earth’s surface(forms from magma).Ex. granite

Rhyolite- extrusive rapid cooling

Granite- Intrusive slow cooling

Composition of Magma A slushy mix of : Molten rock Gases Mineral crystals

Elements in Magma Oxygen (O) Silicon (Si) Aluminum (Al) Iron (Fe) Potassium (K) Sodium (Na) Magnesium (Mg) Calcium (Ca)

Magma is classified based on the amount of silica it contains. SiO2

Types of magma Rhyolitic Andesitic Basaltic 70% 60% 50% Group SiO2 Content Rhyolitic Andesitic Basaltic 70% 60% 50%

Origins of Magma In labs, most rocks melt when they hit 800°C to 1200°C These temps are found in the upper mantle & lower crust Scientists think this heat comes from the decay of radioactive elements & the remaining energy from Earth’s molten formation  

Check Point What is the difference between magma and lava? What are the two types of igneous rocks? Which type of magma has the most silica content?

Factors That Affect Magma Formation 1.Temperature Temp ↑ with depth in Earth’s crust 2. Pressure Pressure ↑ with depth because of the weight of overlying rock As pressure ↑, so does the melting point

4.Mineral’s composition 3.Water content Rocks & minerals contain little water The higher the water content , the lower the melting point 4.Mineral’s composition Different minerals have different compositions and therefore have different melting points

How Rocks Melt Partial Melting – process in which different minerals melt into magma at different temperatures, changing its composition. Some minerals melt, while others remain solid As minerals melt, different elements are added to the magma “stew,” thereby changing its composition

Fractional Crystallization – process in which different minerals crystallize from magma at different temperatures, removing elements from magma. Changes composition of magma by removing elements

Bowen’s Reaction Series Discovered by a geologist named Bowen Sequential, predictable, dual-branched pattern in which minerals crystallize from cooling magma Two main patterns or branches of crystallization 1. Continuous, gradual change of mineral composition Ex. feldspars (change from calcium rich to sodium rich)

Magma is made up of different minerals that crystallize at different temperatures. So during the cooling and crystallization process some minerals become solid while others remain molten.

Bowen’s Reaction continued… 2. An abrupt change of mineral type Iron-rich minerals change into other minerals.   Ex. At 18000C Olive forms once that substance reaches 1557 degrees a new mineral is formed (pyroxene).

Magmatic Differentiation As minerals form in the Bowen series the solid more dense ones fall to the bottom and are not available for the reaction anymore so the material that is available is now different.

Bowens reaction https://www.youtube.com/watch?v=K6aQlYA4BHU www.youtube.com/watch?v=R4X8ukSpbQo https://www.youtube.com/watch?v=ApLp7GMDOE0

Crystal separations Under certain conditions newly formed crystals can be separated from rock that explains why olivine is found in the rock that is why olivine did not convert to pyroxene during cooling.

Layered Intrusions Sometimes during cooling layered intrusions form. Scientist are uncertain why. Maybe temperature differences. Valuable rare metals maybe found here. Ex. Platinum, chromium, nickel, and gold.

Check Point 1. What happens to temperature with depth? 2. As depth increases does pressure decrease or increase? 3. What is partial melting? 4. Summarize Bowen’s reaction?

5.2 Classifying Igneous Rocks Igneous rocks are broadly classified as intrusive or extrusive. However, they are further classified by mineral composition what minerals are found in the rock color grain size

if lava cools quickly then small crystals form Example: Obsidian has no visible mineral grains if magma cools slowly then large crystals form Example: Gabbro has large mineral grains

early forming minerals may have well shaped crystals texture early forming minerals may have well shaped crystals later forming minerals may have irregular shaped crystals porphyritic texture – contains both large & small crystals  

Classification of Igneous Rocks

Four Main Groups of Igneous Rocks 1. Felsic Light colored High silica content Contain quartz, feldspar,orthoclase, and plasioclase Ex, granite

2. Mafic Dark colored Low Silica Plagioclase, biotite, amphibole, pyroxene, and olivine Rich in Iron and Magnesium Example, Gabbro

Contain moderate amounts of biotite, amphibole, pyroxene, and olivine. 3. Intermediate page107 Contain moderate amounts of biotite, amphibole, pyroxene, and olivine. Ex. diorite

4. Ultramafic Low Silica High Iron and Magnesium Ex, Peridotite and dunite

Check Point What are the four mineral composition types and two facts about each? (you have 5 minutes) What is a pegmatite? What is a kimberlite? Answer #6 on p. 106

Igneous Rocks as Resources Igneous rocks are good resources as building materials because of their strength, durability, ability to resist weathering, and beauty.  

Ore Deposits Ore deposits can be found within igneous rocks or in the cracks and voids surrounding the rocks, called veins Dissolved silica & common metals (Ex: gold, silver, lead, copper) are released at the end of magma crystallization in a hot, mineral rich fluid that fills the veins. Fluid solidifies to form metal-rich quartz veins Ex, gold-bearing quartz in Sierra Nevada Mountains in California

Pegmatite- vein deposits of extremely large-grained minerals that can contain rare ores such as lithium and beryllium   Kimberlites – rare, ultramafic rock that contain diamonds and other minerals formed only under very high pressures