1. Igneous Rocks Earth Science Chapter 3 Section 1

2. B ELLWORK : Your five-year-old cousin comes up to you and asks “What are rocks made of?” What do you tell her?

3. T ODAY ’ S O BJECTIVES : ● Briefly explain the crystallization of magma. ● List the criteria used to classify igneous rocks. ● List the names, textures, and environments of formation for the most common igneous rocks. ● Briefly explain Bowen’s reaction series and how it relates to magmatic differentiation.

4. F ORMED BY F IRE ● Magma (molten rock) begins rising to the surface ● If it breaks through, it is called lava ● Cools and the atoms begin to crystallize ● If at surface, called extrusive or volcanic rock ● If below surface, called intrusive or plutonic rock ● How fast the rock cools determines the texture of the final rock

5. C RYSTALLIZATION OF M AGMA ● Ions arrange themselves into orderly patterns ● Crystal size is determined by the rate of cooling ● Slow rate produces large crystals ● Fast rate produces microscopic crystals ● Very fast rate produces glass

6. T EXTURES OF I GNEOUS R OCKS ● Fine-Grained ● Form at surface and cool quickly ● Different types of mineral crystals too small to be seen with unaided eye ● Can have trapped air bubbles called vesicles

7. T EXTURES - C ONTINUED ● Course-Grained ● Form far below the surface and cool very slowly ● Different types of mineral crystals easily seen with unaided eye ● Example: Granite

8. T EXTURES - C ONTINUED ● Porphyritic ● Partially cooled crystals in magma are erupted onto the Earth’s surface ● Large crystals embedded in tiny crystals

9. T EXTURES - C ONTINUED ● Glassy ● Molten rock ejected into the atmosphere ● Cools almost instantly – ions do not have time to crystallize

10. B OWEN ’ S R EACTION S ERIES ● Explains mineral composition of igneous rocks ● Shows the order in which minerals crystallize ● Influenced by crystal settling in the magma

11. N AMING I GNEOUS R OCKS ● Granitic rocks ● Composed almost entirely of light-colored silicates—quartz and feldspar ● Also referred to as felsic: feldspar and silica (quartz) ● High silica content (about 70%) ● Common rock type is granite

12. N AMING I GNEOUS R OCKS ( CONT.) ● Basaltic rocks ● Contain substantial dark silicate minerals and calcium- rich plagioclase feldspar ● Also referred to as mafic: magnesium and ferrum (iron) ● Common rock type is basalt

13. N AMING I GNEOUS R OCKS ( CONT.) ● Other compositional groups ● Andesitic (Intermediate) rocks ● Have a composition between that of a granitic and a basaltic rock ● Associated with volcanic activity typically confined to margins of continents

14. N AMING I GNEOUS R OCKS ( CONT.) ● Ultramafic ● Contains mostly dark-colored silicates, like olivine and pyroxene ● Rare at Earth’s surface, but believed to be main component of the upper mantle