Identifying Igneous Rocks - PowerPoint PPT Presentation

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Identifying Igneous Rocks

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  1. Identifying Igneous Rocks

  2. Rock Types • A rock is a group of minerals bound together Igneous Rock Sedimentary Metamorphic

  3. Igneous Rocks • form when magma cools and hardens • = “Fire Formed” • random fabric of fused mineral grains • http://www.youtube.com/watch?v=eoPz5O6_-d0&feature=related

  4. Igneous Rock Types • Intrusive = form inside the Earth • magma cools slowly to create large crystals • Extrusive = form on the Earth’s surface • lava cools quickly to create small crystals

  5. Which is which? How do you know? Extrustive: Small Crystals Intrusive: Large Crystals

  6. 2 Types of Magma • Felsic : light color, high silica, viscous (thick and slow), low metals • Felsic – Feldspar + Silica • Mafic – Dark color, low silica, not viscous (thin and watery), high metals • Mafic = Magnesium + Iron (Fe)

  7. Which is which? How do you know? Mafic: Dark overall color Felsic: Light overall color

  8. Texture = Crystal Size Fine grained = crystals are too small to see Coarse grained = crystals are easily visible basalt granite

  9. Which is which? How do you know? Fine: small crystals Coarse: Large crystals

  10. Other textures • Glassy= rock freezes instantly. There are no crystals (obsidian) • Porphyritic large crystals surrounded by fine-grained crystals (rhyolite) • Vesicular: fine grained, felsice, vesicular volcanic igneous rock(pumice)