Igneous Rocks

Magma is the molten rock material below the surface.

•Lower density causes magma to rise toward the surface (compared to the surrounding rock).

•Magma at the surface is lava.

•Igneous rocks are formed from solidified/cooled magma or lava.

•Igneous rocks are made of interlocking crystals

Igneous Rock

Igneous RocksMagma extruded onto the Earth’s surface forms volcanic or extrusive igneous rocks.

Magma that crystallizes within the Earth’s crust forms plutonic or intrusive igneous rock.

Extrusive & Intrusive Igneous Rocks

• Intrusive- Magma under the surface– Coarse-grained (igneous rock)– Magma cools slowly and large crystals grow over a long period of time

– Gabbro, diorite, granite

Extrusive & Intrusive Igneous Rocks

• Extrusive- Lava at the surface– Fine-grained (igneous rock)– Lava cools very quickly, consequently crystals do not have time to grow and develop

– Basalt, andesite, rhyolite, obsidian

Igneous Rocks

Molten rock or magma(1,000-1,200 oC), contains chemical elements.

If the magma begins to cool, elements begin to form chemical bonds within the magma and crystals start to develop.

Igneous RocksThe crystallization of magma fluids, either through extrusive or intrusive processes, creates the minerals that make up igneous rocks.

All rocks are composed of minerals, and minerals are composed of one or more chemical elements.

Igneous RocksThe primary elements that make up rock-forming minerals are: -Silicon (Si)-Oxygen (O)-Iron (Fe)-Magnesium (Mg)-Potassium (K)-Sodium (Na)-Calcium (Ca) Various combinations of these elements form the most common mineral group, the silicates. The most important silicate minerals are quartz, feldspar, mica, amphibole, pyroxene, and olivine.

Igneous Rocks

As magma cools slowly, elements within it become chemically bonded forming crystals of minerals.

However, not all minerals form at the same time during the cooling process. Some minerals crystallize when magma is at a higher temperature, while others only crystallize when magma is at a lower temperature.

Bowen's Reaction Series describes when the eight most common silicate minerals form during the cooling process.

Igneous Rocks

Igneous Rocks

Rocks that form from magma or lava cooled from high temperatures tend to contain a lot of iron and magnesium but little silica. These rocks are called mafic and tend to be dominated by dark colored minerals such as amphibole and pyroxene (Elements: iron & magnesium).

Igneous Rocks

When magma cools slowly, minerals that form at cooler temperatures dominate the resulting rock. These rocks are called felsic and tend to be light colored with minerals such as feldspar and quartz. (Elements: silicon, oxygen, sodium, potassium, & aluminum)

Igneous Rocks

Igneous Rocks

Igneous Rocks

Classification of Igneous Rocks-Texture: crystal size-Color-Mineral composition

Igneous Rocks

Granite•Felsic•Intrusive

Igneous Rocks

Rhyolite•Felsic•Extrusive

Igneous Rocks

Basalt•Mafic•Extrusive

Igneous Rocks

Gabbro•Mafic•Intrusive

Igneous Rocks

Andesite•Intermediate•Extrusive

Igneous Rocks

Diorite•Intermediate•Intrusive

Igneous Rocks

Other Igneous Rocks• Lava flows• Fragmented magma ejected explosively– Ash plumes– Pyroclastic flows

• Cool and solidify very quickly; no minerals developConsequently they cannot be mafic, intermediate, or felsic

Igneous Rocks

Obsidian•Extrusive

Igneous Rocks

Pumice•Extrusive