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Igneous Rocks

Mrs. Griffin. Igneous Rocks. Igneous uses and resources. Granite, very durable. Rhodes Memorial in Cape Town, South Africa…..De Beers? Cecil Rhodes Vietnam Memorial. What are igneous rocks?. Igneous rocks are formed from the crystallization of magma.

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Igneous Rocks

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  1. Mrs. Griffin Igneous Rocks

  2. Igneous uses and resources • Granite, very durable. • Rhodes Memorial in Cape Town, South Africa…..De Beers? • Cecil Rhodes • Vietnam Memorial

  3. What are igneous rocks? • Igneous rocks are formed from the crystallization of magma. • Lava is magma that flows out onto Earth’s surface.

  4. Types of Igneous Rocks • Extrusive- fine-grained, that cool on Earth’s surface. • Intrusive-coarse-grained, that cool slowly beneath Earth’s surface. • Granite

  5. Composition of Magma • Slushy mix of molten rock, gases, and mineral crystals. • Elements are the same as the major elements found in Earth’s crust: O, Si, Al, Fe, Mg, Ca, K, Na. • Silica (SiO2) is the most abundant compound found in magma. Magmas are classified as basaltic , andesitic, and rhyolitic based on the amount of silica they contain: • Basaltic 50%, andesitic 60%, rhyolitic 70%

  6. Factors that Affect Magma Formation • Temperature, pressure, water content, and mineral composition. • Temperature and pressure/Earth’s crust: increase or decrease? • Water-> changes the melting point of rocks; as water content increases, the melting point decreases. • Different minerals have different melting points.

  7. How do rocks melt? • Water, candle wax, and ice tray. • Rocks contain different minerals and therefore have different melting points….this is why magma is often slushy. • Partial melting: where some minerals melt at low temperatures while others remain solid. • Fractional crystallization: the process where different minerals form at different temperatures. • The 1st minerals to crystallize from magma are the last minerals to melt during partial melting.

  8. Classifying Igneous Rocks • Further classify by mineralcomposition: 3 main groups of igneous rocks: • Felsic- granite, light-colored, & have high silica content, and contain quartz and the feldspars orthoclase and plagioclase. • Mafic rocks-include gabbro, dark colored, lower silica contents, rich in iron and magnesium. • Ultramafic- peridotite and dunite, have low silica content and high levels of iron and magnesium. • Diamonds are found in ultramafic rocks known as kimberlites. • Kimberly Diamond Mine in South Africa

  9. Classifying Igneous Rocks cont. • Grain size- obsidian no visible mineral grains vs. gabbro. • Texture, such as glassy. • Porphyritic texture- characterized by large, well-formed crystals surrounded by finer grained crystals of the same mineral or different minerals.

  10. Review • What are igneous rocks? How are they formed? • Compare and contrast intrusive/extrusive rocks? • What is partial melting? • Explain fractional crystallization.

  11. Mrs. Griffin Sedimentary & Metamorphic Rocks

  12. Formation of Sedimentary Rocks • Much of Earth’s surface is covered with sediments- pieces of solid material that have been deposited on Earth’s surface by wind, water, ice, gravity, or chemical precipitation. • Up or down? • When these sediments become cemented together they form sedimentary rocks. This process begins when weathering and erosion produce sediments.

  13. Weathering • A set of physical and chemical processes that break rock into smaller pieces. • Produces rock and mineral fragments known as clastic sediments. How is a solid rock formed from clastic sediments? • Weathering • Erosion and transport • Deposition • Burial and lithification

  14. Features of sedimentary rocks • The primary feature of sedimentary rocks is bedding. • Graded bedding- particle sizes become progressively heavier and coarser towards the bottom layer. • Cross bedding- inclined layers of sediment move forward across a horizontal surface.

  15. Features continued • The best-known features of sedimentary rocks is what??? • Fossils

  16. Types of Sedimentary Rocks • The most common type of sedimentary rocks are clastic rocks. These can be further classified according to the sizes of their particles. • Coarse-grained- breccia • Medium-grained- sandstone, an important feature: porosity, the % of open spaces b/w grains in a rock. • Fine-grained- siltstone.

  17. Metamorphic Rocks • When rocks are buried at great depths, pressure and temperature increase -> rocks melt and form magma. • What happens if they don’t get to this point? • Rock will change form while remaining solid, metamorphism. • When high temperature and pressure affect large region’s of the Earth’s crust they produce large belts of regional metamorphism.

  18. Metamorphic Textures • Classified into two textural groups: • Foliated- wavy layer and bands of minerals, schist and gneiss. • Nonfoliated- lack mineral grains with long axes in one direction, quartzite and marble.

  19. The Rock Cycle • The continues changing and remaking of rocks.

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