- Slides: 17
Igneous Rock Classification Dr. David Steer
Analysis Time Ü Given: Bag rocks Group these rocks in some manner
Color (Proxy for silica content) Grouping items Ü Group Size (Proxy for grain size) these objects in some logical way.
Grouping items Ü Group these objects in some logical way.
Analysis time Ü Given: Bag rocks Group these rocks in some manner
Igneous Rocks Ü Volcanic v. Cool (extrusive) igneous rocks fast, small crystals vform when molten rock (magma) in the earth’s interior rises to the surface through pipes or fractures in the crust.
Igneous Rocks v Plutonic v. Cool vform (intrusive) igneous rocks slow, large crystals 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 Ü Texture size of crystals most important Cooling rates – Surface, fast w Small crystals – Below surface slow w Larger crystals a) Which formed at surface? Both are the same chemistry b) Rhyolite Granite
Chemical Composition Ü Color Indicative of chemistry and temperatures of formation – Dark colors w High temperatures (1000 to 1200 o. C) w Low silica content Which is the high silica rock? – Light colors Both formed below the surface w Lower temperatures w High silica content a) b) Gabbro Granite
Texture Ü So explain this!!!!
Six common Igneous Rocks 1000 C Solidifying Temperature 500 C Increasing Grain Size Minerals Plutonic Present (in order of Rocks abundance) pyroxene, olivine, feldspar, & amphibole Gabbro Andesit intermedi e ate feldspar, amphibole, pyroxene, biotite mica Diorite Rhyolite high feldspar, Granite Lighter Color Volcani Silica c Content Rocks Basalt low
Draw a concept map that guides you through classifying an igneous rock. Use these terms to: Classify Igneous Rocks Basalt Cool Slow Gabbro Large Grain Plutonic Small Grain Color Cool Quick Dark Extrusive Granite High Silica Low Silica Light Texture Rhyolite
Identify the rock type associated with the diagram below. Question 1) 2) 3) 4) a. b. c. d. 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. What information would you no longer be able to infer? a. texture c. composition b. cooling rate
Analysis Time Ü Given: Bag rocks Identify the rocks