Igneous Rock Classification Dr. David Steer

Rock cycle

Analysis Time Given: Bag rocks Group these rocks in some manner

Grouping items Group these objects in some logical way. Color (Proxy for silica content) Size (Proxy for grain size) Group these objects in some logical way.

Grouping items Group these objects in some logical way.

Analysis time Given: Bag rocks Group these rocks in some manner

Rock Cycle

Igneous Rocks Volcanic (extrusive) igneous rocks Cool fast, small crystals form when molten rock (magma) in the earth’s interior rises to the surface through pipes or fractures in the crust.

Igneous Rocks Plutonic (intrusive) igneous rocks Cool slow, large crystals form when magma cools within the earth. Igneous rocks that cool below the earth's surface are termed plutonic (or intrusive) igneous rocks.

Classification of Igneous rocks Texture size of crystals most important Cooling rates Surface, fast Small crystals Below surface slow Larger crystals Which formed at surface? Both are the same chemistry a) b) Rhyolite Granite

Chemical Composition Color Indicative of chemistry and temperatures of formation Dark colors High temperatures (1000 to 1200 oC) Low silica content Light colors Lower temperatures High silica content Which is the high silica rock? Both formed below the surface a) b) Gabbro Granite

Texture So explain this!!!!

Six common Igneous Rocks Solidifying Temperature 500 C Increasing Grain Size Volcanic Rocks Silica Content Minerals Present (in order of abundance) Plutonic Rocks Basalt low pyroxene, olivine, feldspar, & amphibole Gabbro Andesite intermediate feldspar, amphibole, pyroxene, biotite mica Diorite Rhyolite high feldspar, quartz, muscovite mica, & amphibole Granite Lighter Color

Basalt Color Cool Quick Cool Slow Dark Extrusive Draw a concept map that guides you through classifying an igneous rock. Use these terms to: Classify Igneous Rocks Basalt Color Cool Quick Cool Slow Dark Extrusive Gabbro Granite High Silica Large Grain Low Silica Light Plutonic Texture Rhyolite Small Grain

Identify the rock type associated with the diagram below. Question Plot 1 Plot 2 Plot 3 Plot 4 andesite porphory gabbro basalt obsidian

5) Imagine that all minerals found in rocks were the same color 5) Imagine that all minerals found in rocks were the same color. What information would you no longer be able to infer? a. texture b. cooling rate c. composition

Analysis Time Given: Bag rocks Identify the rocks