3.2 – Igneous Rocks

Videos/Websites http://www.youtube.com/watch?v=7FLlccELWUo http://geology.com/rocks

Do Now What are the two ways igneous rocks are formed?

Do Now What are the two ways igneous rocks are formed? Intrusive (beneath Earth’s surface) Extrusive (above Earth’s surface)

Texture Classified Key Words

Vocab Words Intrusive Igneous Rock Extrusive Igneous Rock Porphyritic Texture Vocab Words

Igneous Rocks Commonly known as “fire” or “volcano” rocks. Igneous rocks are formed when magma under the surface cools, and when lava cools at the surface. Intrusive vs. Extrusive

Intrusive Igneous Rocks Igneous rocks that form when magma hardens beneath Earth’s surface. Large crystals form. Only reason we see these rocks is because of erosion. The erosion breaks away layers above the intrusive igneous rocks. Diorite Gabbro Granite Pegmatite Peridotite

Extrusive Igneous Rocks Igneous rocks that form when lava hardens on Earth’s surface. Andesite Basalt Obsidian Pumice Rhyolite Scoria Komatiite (rare) Tuff (Ejected fragments from a volcanic eruption)

Classification of Igneous Rocks Texture and composition are two characteristics used to classify igneous rocks. Texture describes the appearance of an igneous rocks based on its size, shape, and the arrangement of its interlocking crystals. The composition classes of igneous rocks are based on the proportions of light and dark minerals in the rock.

Texture Coarse-Grained Fine-Grained Slow cooling results in the formation of large crystals. Fine-Grained Rapid cooling results in small, interconnected mineral grains.

Texture Glassy Porphyritic When there is not enough time for the ions in the lave to arrange themselves into a network of crystals. Porphyritic Rocks with different rates of cooling, with large crystals surrounded by fine grains.

Composition Granitic Basaltic Made almost entirely of the light-colored silicate minerals quartz and feldspar. Basaltic Made almost mostly of dark silicate minerals and plagioclase feldspar. Rich in magnesium and iron. Darker and denser than granitic compositional rocks.

Composition Andesitic Ultramafic Rocks with a composition in between granitic and basaltic. 25% dark silicate minerals. Ultramafic Composed almost entirely of dark silicate minerals. These are rare.

Classification Chart

Group Activity On page 74, use that table to fill in the blanks on your group paper and place it in your folder when complete.