Igneous Rocks

What You Need to Learn

n How magma melts and crystallizes to form igneous rocks

n How igneous rocks are classified

n How igneous rocks are used

What are Igneous Rocks?

n Formed from crystallization of magma

n Latin for “fire”

n Types:

n Extrusive: formed when magma flows to the Earth’s surface and cools quickly

n Fine grained

n Intrusive: formed from slowly cooled magma in the Earth’s crust

n Coarse grained

Magma

n Slushy mix of molten rock, gases, and mineral crystals

n 3 basic types: Rhyolitic, Andesitic, Basaltic

n Formed in the upper mantle and lower crust @ temperatures of 800-1200°C

n Magma temperature, pressure, water content, and mineral composition effect formation

How Do Rocks Melt?

n Partial melting: minerals have different melting points, therefore melt at different temperatures

n Fractional Crystallization: magma crystallizes in the reverse order of partial melting

Bowen’s Reaction Series

n Minerals form in predictable patterns

n Fledspar minerals: as cooling occurs minerals go from calcium rich to sodium rich

n Iron-Rich minerals: abrupt mineral transitions occur; olivine converts to pyroxene

Classification

Igneous Rocks as Resources

n Building materials

n Strong

n Resistant to weathering

n Durable

n Gold, silver, lead, and copper are often found in veins in igneous rock

n Pegmatites that contain lithium and beryllium

n Kimberlites that contain diamonds