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Igneous Rocks Niti Mankhemthong

Igneous Rocks Niti Mankhemthong. Modified from http://www.authorstream.com/Presentation/kcollazo-170754-igneous-rocks-science-education-ppt-powerpoint/. Igneous Rocks. Igneous rocks form when magma cools and hardens.

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Igneous Rocks Niti Mankhemthong

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  1. Igneous RocksNitiMankhemthong Modified from http://www.authorstream.com/Presentation/kcollazo-170754-igneous-rocks-science-education-ppt-powerpoint/

  2. Igneous Rocks Igneous rocks form when magma cools and hardens. Igneous from the Latin meaning “Fire formed”, is a rock type that forms from the solidification of a molten mineral solution. Photo used with permission from Mike Jarvis, Naperville Central HS, Naperville, IL

  3. All igneous rocks have a random fabric of fused mineral grains.

  4. Igneous Rocks • Intrusive (Plutonic)rocks form inside the Earth (underground) when magma cools slowly to create large crystals. • (Intrusive = Inside) • Extrusive (Volcanic)rocks form on the Earth’s surface (above ground) when lava cools quickly to create small crystals. • (Extrusive = Exit/outside)

  5. Intrusive: Large crystals Which is which? How do you know? Extrusive: Small crystals

  6. Igneous Rocks • There are 3 types of igneous rocks 1. Felsic= Light color, high in silica, viscous (thick and slow), low in iron, calcium or magnesium Felsic=Feldspar+ Silica 2. Mafic= Dark color, low in silica, not viscous (thin and watery), high in iron, calcium and magnesium Mafic=Magnesium + Iron (Fe) 3. Ultramafic= Very dark in Color

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

  8. Igneous Rocks • Texture refers to the crystal size. • Textures are divided into five main types: 1. Fine-grained (aphanitic) • crystals are invisible or hard to see with the naked eye • They often have cooling cracks. • They make poor building materials. • Such as basalt

  9. 2. Coarse-grained (Phaneritic) • Crystals are easily visible (granite) • Crystals fit together • They are generally the strongest igneous rocks due to interlocking btw grains • Such as granite

  10. Coarse Grained: Large crystals Which is which? How do you know? Fine Grained: Small crystals

  11. 3. Aporphyritictexture • is a rock with large crystals surrounded by fine-grained crystals. • Large and small crystal are not touching each other. It is easy to confuse a porphyritic rock with a phaneritic rock. • Porphyritic rocks are both intrusive and extrusive. This is a porphyriticandesite similar to the rocks we see on the campus.

  12. Porphyritic Texture: Rhyolite: Light colored (felsic), fine grained (volcanic) igneous rock

  13. Igneous Rocks 4. Aglassytexture • like broken glass, and you can’t see any grains, no matter how hard you try (no crystal). • This magma cools so quickly that crystals have no time to form at all. • Glasses are not very stable, since they are not crystalline. They are not a good aggregate for concrete or good building stones, because they take on water.

  14. Glassy Texture: Volcanic Glass/Obsidian: is usually mafic. Even when felsic it appears dark nonetheless because the small % of mafic minerals in the rock form a homogenous solution with the felsic minerals tinting the overall color to dark. Notice the conchoidal fracture.

  15. 5. Vesicular: • Vesiclesare holes, so a vesicular rock is a “holey” rock. • The holes are formed when gas and other volatiles escape the lava before it hardens. • Vesicular rocks are extrusive origin. • The holes make the rock weak, and it is therefore a poor building material. • This material is often used for landscaping/xeriscaping in the El Paso area.

  16. Vesicular Texture: Pumice: Fine grained, felsic, vesicular volcanic igneous rock. Scoria: Fine grained, mafic, vesicular volcanic igneous rock.

  17. Igneous Rocks Rocks can be grouped into families: • Granite family = felsic, light, contains quartz, feldspar, & muscovite. (granite, rhyolite, obsidian, pumice) • Gabbro family = mafic, dark, contains feldspar, olivine, biotite. (gabbro, basalt, scoria) • Diorite family = intermediate composition and color. (diorite, andesite, obsidian)

  18. Warming up!! Let’s try some examples, tell me if the following rock samples are: 1. Felsic or Mafic 2. Fine grained or Coarse grained 3. Intrusive or Extrusive Be sure to tell me how you knew.

  19. Basalt Mafic = Dark color Fine grained= Small crystals Extrusive= Small crystals = Formed on surface

  20. Diorite Felsic = Light color Coarse grained= Large crystals Intrusive = Large crystals = Formed underground

  21. Gabbro Mafic = Dark color Coarse grained= Large crystals Intrusive= Large crystals = formed underground

  22. Pumice Felsic = Light color Fine grained= Small crystals Extrusive= Small crystals = Formed above ground

  23. Scoria Mafic = Dark color Fine grained= Small crystals Extrusive= Small crystals = Formed above ground

  24. Remember: Safety First!!! Intermission

  25. Mineralogy Textures Textures

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