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Don’t you wish you were here?

Don’t you wish you were here?. The Rock Cycle. Igneous Rocks. THE ROCK CYCLE. Rocks are naturally occurring combinations of minerals, fossils or other hard materials. They are classified by the way in which they form. The three rock types are: igneous, sedimentary and metamorphic.

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Don’t you wish you were here?

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  1. Don’t you wish you were here?

  2. The Rock Cycle Igneous Rocks

  3. THE ROCK CYCLE Rocks are naturally occurring combinations of minerals, fossils or other hard materials. They are classified by the way in which they form. The three rock types are: igneous, sedimentary and metamorphic. All rocks on Earth are locked into a system of cycling and re-cycling known as the ROCK CYCLE. (*)

  4. Earth as a system: The rock cycle

  5. Igneous Rocks • Form as magma cools and crystallizes • Rocks formed inside Earth (intrusive) rocks • Rocks formed on the surface (extrusive) rocks

  6. Magma • The nature of magma • Consists of three components: • A liquid portion, called melt, that is composed of mobile ions • Solids, if any, are silicate minerals that have already crystallized from the melt • Volatiles, which are gases dissolved in the melt, including water vapor

  7. Magma • Crystallization of magma • Crystal size is determined by the rate of cooling • Slow cooling = large crystals • Fast cooling = microscopic crystals • Very fast cooling = glass

  8. Magma • Crystallization of magma • Texture in igneous rocks is determined by the size and arrangement of mineral grains • Igneous rocks are typically classified by • Texture • Mineral composition

  9. Igneous textures • Fine-Grained or (Aphanitic) • Rapid rate of cooling • Microscopic crystals • May contain holes from gas bubbles • Typically occurs in extrusive / volcanic rocks • Example is Rhyolite

  10. Igneous textures • Course-Grained or (Phaneritic) • Slow cooling • Crystals can be identified without a microscope • Typically occurs in intrusive / plutonic rocks • Example is granite

  11. Igneous textures • Large Crystals or (Porphyritic) • Minerals form at different temperatures as well as differing rates • Large crystals, called phenocrysts, are embedded in a matrix of smaller crystals, called the groundmass

  12. Igneous textures • Glassy texture • Very rapid cooling of molten rock • Resulting rock is called obsidian

  13. Igneous textures • Vesicular • Cellular; full of holes; often light weight. • Example is Pumice.

  14. Igneous Textures • Fragmental • Composed of fragments ejected during a volcanic eruption • Varieties • Tuff – ash-sized fragments • Volcanic breccia – particles larger than ash

  15. Igneous Compositions • Composed mainly of silicate minerals • Dark silicates = rich in iron and/or magnesium, creates dark rocks • Olivine • Pyroxene • Amphibole • Biotite mica • Light silicates = greater amounts of potassium, sodium, and calcium, creates light colored rocks • Quartz • Muscovite mica • Feldspars

  16. Igneous Compositions • Igneous rocks are often classified by mineral (chemical) composition • Mafic (or basaltic))= Dark colored • Felsic (or granitic)= Light colored

  17. ~ End ~

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