1. Chapter 5

2. Lava: magma that flows out onto Earth’s surface.  Igneous rocks : formed from the crystallization of magma. What are igneous rocks?  Magma : slushy mix of molten rock, gases, and mineral crystals. elements found in magma : oxygen (O), silicon (Si), aluminum (Al), iron (Fe), magnesium (Mg), calcium (Ca), potassium (K), and sodium (Na). (Do these look familiar?)

3.  Extrusive : fine-grained igneous rocks that cool quickly on Earth’s surface. What are igneous rocks? Intrusive : coarse-grained igneous rocks that cool slowly beneath Earth’s surface. Granite is the most common intrusive igneous rock.

4.  Careful study of granite rock formations revealed that they cut across other rock formations. What are igneous rocks? cross-cutting relationships are evidence that the granite was intruded, or forced into, existing rocks. Magma cools slowly beneath Earth’s surface and forms course-grained igneous rocks such as granite.

5. Factors That Affect Magma Formation What are igneous rocks? temperature pressure water content mineral composition.

6. Factors That Affect Magma Formation What are igneous rocks? geothermal gradient: Temperature generally increases with depth in Earth’s crust Pressure also increases with depth (WhERE DOES THIS PRESSURE COME FROM?). –Pressure and melting point have a direct relationship (DRAW A GRAPH FOR THIS) –Water content and melting point have an inverse relationship (DRAW A GRAPH FOR THIS) –Mineral content also impacts how magma is formed as different minerals have different melting points. – For rocks to melt, the right combination of temperature, pressure, and composition must be present.

7. What are igneous rocks? –Partial melting –some minerals melt at low temperatures while other minerals remain solid. Why? –different minerals have different melting points, not all parts of a rock melt at the same time

8. Fractional Crystallization What are igneous rocks? –When magma cools, it crystallizes in the reverse order of partial melting –This means: the first minerals to crystallize from magma are the last minerals to melt during partial melting.

9.  illustrates the relationship between cooling magma and mineral formation. What are igneous rocks? two main patterns/branches –1. continuous, gradual change of mineral compositions in the feldspar group. –2. abrupt change of mineral type in the iron- magnesium groups.

10. What are igneous rocks? –***As minerals form elements are removed from the magma. –****Silica and oxygen are left over at the end of the reaction series –Because silica and oxygen have low melting points, they crystallize last and form QUARTZ.

11. –Layered igneous intrusions can be valuable sources of rare metals: Layered Intrusions What are igneous rocks? Platinum Chromium Nickel Gold

12.  Igneous rocks are classified by :  intrusive or extrusive. Classifying Igneous Rocks  mineral compositions.  Physical properties:  grain size  texture serve

13.  3 Main Mineral Groups of Igneous Rocks: Classifying Igneous Rocks –Felsic : light-colored; high silica contents. –Ex. Granite –Mafic : dark-colored; lower silica contents; rich in iron and magnesium. –Ex. Gabbro –Intermediate rocks, have some characteristics of both felsic and mafic rocks. –Ex. Diorite (dark, high silica) –Ultramafic low silica contents and very high levels of iron and magnesium.

14. Classifying Igneous Rocks

15. Cooling Rates –Extrusive igneous rocks have no visible mineral grains. –Intrusive igneous rocks may have crystals larger than 1 cm.; beneath Earth’s surface, there is sufficient time for large crystals to form.

16. Porphyritic Texture Classifying Igneous Rocks –large, well-formed crystals surrounded by finer- grained crystals of the same mineral or different minerals. –indicates a complex cooling history wherein a slowly cooling magma suddenly began cooling rapidly.

17.  Igneous rocks have several characteristics that make them especially useful as building materials. Classifying Igneous Rocks –Strength: interlocking grain textures Many of the --- –minerals in these rocks are resistant to weathering.

18.  Remember that Ores are minerals that contain a useful substance that can be mined at a profit? Classifying Igneous Rocks Valuable ore deposits are often associated with igneous intrusions. These deposits sometimes occur as veins –These elements, along with the dissolved silica, are released at the end of magma crystallization in a hot, mineral-rich fluid that fills cracks and voids in the surrounding rock. –This fluid solidifies to form metal-rich quartz veins, such as the gold-bearing veins.

19. Pegmatites Classifying Igneous Rocks –extremely large-grained minerals. –Ores of rare elements, such as lithium and beryllium, are found in pegmatites. –Because these veins fill cavities and fractures in rock, minerals grow into voids and retain their shapes.

20. Kimberlites Classifying Igneous Rocks –Ultramafic –May contain Diamond –Minerals found in kimberlites can form only under very high pressures.