1. Table of Contents Title: Classification of Igneous Rocks Page #: 33 Date: 11/26/2012

2. Objective  Students will be able to classify different types of textures of igneous rocks.  Students will be able to recognize the effects of cooling rates on grain size in igneous rocks.  Students will be able to describe some uses of igneous rocks.

3. Word of the Day:  Composition: The combining of parts to make a whole.  Coarse: Rough to the touch.  Fine: Very small.

4. Classification of Igneous Rocks  ***Main Idea***: Classification of Igneous Rocks is based on  Mineral composition  Crystal size  Texture

5. Mineral Composition of Igneous Rocks  Intrusive Rocks: Rocks that form below Earth’s surface.  Have large crystals.  Extrusive Rocks: Rocks that form on Earth’s surface.  Have small crystals.

6. Mineral Composition of Igneous Rocks  Basaltic Rocks: Dark in color, low silica content, mostly contain the minerals plagioclase and pyroxene.  Example: Gabbro  Granitic Rocks: Light in color, high in silica content, mostly contain the minerals quartz, potassium feldspar and plagioclase feldspar.  Example: Granite  Intermediate Rocks: Between basaltic and granitic rocks. Mostly contain minerals plagioclase feldspar and horneblende.  Example: Diorite

7. Texture of Igneous Rocks  Texture: The size, shape, and distribution of the crystals or grains that make up a rock.  Examples:  Obsidian - “glassy” or “extremely fine-grained”  Rhyolite - “fine-grained”  Granite - “coarse-grained”  Differences in grain size are because obsidian and rhyolite are extrusive rocks and granite is an intrusive rock.

8. Crystal Size and Cooling-Rates of Igneous Rocks  Extrusive Rocks - Cool too quickly for large crystals to form.  Intrusive Rocks - Cool slowly, so large crystals have time to grow.  Porphyritic Rocks: Rocks that have both large and small crystals - “Porphyritic Texture.”  Happens when slow cooling magma suddenly cools very quickly.  Vesicular Rocks: Spongy appearance (holes) - “Vesicular Texture.”  Happens when lava is so thick that escaping gasses form bubbles in it.  Example: Pumice