What are igneous rocks? SWBAT compare and contrast intrusive and extrusive igneous rocks; describe the composition of magma; discuss the factors that affect how rocks melt and crystallize

Get your lab notebook Write a description of the rocks you are shown: Using the hand lens take a closer look, and describe what you see: Draw a picture of what you saw through the hand lens. How many different minerals did you see? What minerals can you identify? Do you see any evidence that these minerals crystallized form molten rock? Explain.

How are igneous rocks formed? Magma –Molten rock under Earth’s surface Lava –Magma that flows out onto Earth’s surface Igneous rocks are formed when magma cystalizes

Types of Igneous Rocks Extrusive –Rocks that form from lava solidifying on Earth’s surface –They are generally fine grained due to quick cooling Intrusive –Rocks that form from magma cooling underground –Generally coarser grained because of the longer cooling time

Magma What is magma composed of? –Slushy mix of molten rock, gases, and mineral crystals What elements does it contain? –Oxygen, silicon, aluminum, iron, magnesium, calcium, potassium, and sodium What are the 3 types of magma? –Basaltic – 50 % SiO 2 –Andesitic – 60% SiO 2 –Rhyolitic - 70% SiO 2 What affects magma characteristics? –Silica - SiO 2

List and describe the 4 factors that affect magma formation Temperature Pressure Water content Mineral composition Temperature increases with depth in crust (geothermal gradient) Pressure increases with depth in crust due to overlying rock. As pressure increases, so does the melting point As water content increases, the melting point of a rock decreases Different minerals have different melting points

Definitions Partial melting –Not all parts of a rock melt at the same time because different minerals have different melting points Fractional crystallization –Different minerals form at different temperatures as a rock cools (opposite order that they melt in) Layered Intrusions –Minerals form into distinct bands in the order shown in Bowen’s reaction series

Bowen’s reaction series Illustrates the relationship between cooling magma and crystal formation. –First pattern Characterized by a continuous gradual change of mineral composition in the feldspar group –Second pattern Characterized by an abrupt change of mineral type in the iron-magnesium groups