EARTH SCIENCE. Geology, the Environment and the Universe. Chapter 5: Igneous Rocks

Size: px

Start display at page:

Download "EARTH SCIENCE. Geology, the Environment and the Universe. Chapter 5: Igneous Rocks"

Belinda Parks
5 years ago
Views:

1 EARTH SCIENCE Geology, the Environment and the Universe Chapter 5: Igneous Rocks

2 CHAPTER 5 Igneous Rocks Section 5.1 What are igneous rocks? Section 5.2 Classification of Igneous Rocks Click a hyperlink to view the corresponding slides. Exit

3 5.1 What are igneous rocks? Essential Questions How do igneous rocks form? How can the composition of magma be described? What are the factors that affect how rocks melt and crystallize?

4 5.1 What are igneous rocks? Igneous rocks are the rocks that form when molten material cools and crystallizes. Review Vocabulary silicate: mineral that contains silicon and oxygen, and usually one or more other elements

5 5.1 What are igneous rocks? New Vocabulary lava igneous rock partial melting Bowen s reaction series fractional crystallization

6 5.1 What are igneous rocks? Igneous Rock Formation Lava is magma that flows out onto Earth s surface. Igneous rocks form when lava or magma cools and minerals crystallize.

7 5.1 What are igneous rocks? Igneous Rock Formation Composition of magma The type of igneous rock that forms depends on the composition of the magma, which is often a slushy mix of molten rock, dissolved gases, and mineral crystals.

8 5.1 What are igneous rocks? Igneous Rock Formation Composition of magma Magma is classified as basaltic, andesitic, or rhyolitic, based on the amount of silica it contains. Silica affects melting temperature and impacts how quickly magma flows.

9 5.1 What are igneous rocks? Please click the image above to view the interactive table.

10 5.1 What are igneous rocks? Igneous Rock Formation Magma formation Magma can be formed either by melting of Earth s crust or by melting within the mantle.

11 5.1 What are igneous rocks? Igneous Rock Formation Magma formation The four main factors involved in the formation of magma are temperature, pressure, water content, and mineral content.

12 5.1 What are igneous rocks? Igneous Rock Formation Magma formation Temperature generally increases with depth in Earth s crust. This temperature increase is known as the geothermal gradient.

13 5.1 What are igneous rocks? Igneous Rock Formation Magma formation Pressure also increases with depth as a result of the weight of overlying rock. The increased pressure on a rock also increases the rock s melting point.

14 5.1 What are igneous rocks? Igneous Rock Formation Magma formation Rocks and minerals often contain small percentages of water, which changes the melting point of the rocks. As water content increases, the melting point decreases.

15 5.1 What are igneous rocks? Igneous Rock Formation Mineral content Rocks melt at lower or higher temperatures because their component minerals have lower or higher melting points. In general, rocks that are rich in iron and magnesium melt at higher temperatures than rocks that contain higher levels of silicon.

16 5.1 What are igneous rocks? Igneous Rock Formation Partial melting The process whereby some minerals melt at relatively low temperatures while other minerals remain solid is called partial melting.

17 5.1 What are igneous rocks? Igneous Rock Formation Partial melting If temperatures are not high enough to melt the entire rock, the resulting magma will have a different composition than that of the original rock.

18 5.1 What are igneous rocks? Bowen s Reaction Series Canadian geologist N. L. Bowen demonstrated that as magma cools and crystallizes, minerals form in predictable patterns in a process now known as the Bowen s reaction series.

19 5.1 What are igneous rocks? Bowen s Reaction Series Bowen discovered two main patterns, or branches, of crystallization.

20 5.1 What are igneous rocks? Bowen s Reaction Series Iron-rich minerals The left branch of Bowen s reaction series represents the iron-rich minerals, which undergo abrupt changes as magma cools and crystallizes.

21 5.1 What are igneous rocks? Bowen s Reaction Series Feldspars The right branch of Bowen s reaction series represents the plagioclase feldspars, which undergo a continuous change of composition as magma cools.

22 5.1 What are igneous rocks? Fractional Crystallization When magma cools, the first minerals that crystallize are the last minerals that melted during partial melting. This process is called fractional crystallization.

23 5.1 What are igneous rocks? Visualizing Fractional Crystallization and Crystal Settling In the basaltic intrusion of the Palisade Sills in the Hudson River valley of New York and New Jersey, small crystals formed in the chill zone as the outer areas of the intrusion cooled more quickly than the interior.

24 5.1 What are igneous rocks? Please click the image above to view the video.

25 5.1 What are igneous rocks? Fractional Crystallization Under certain conditions, newly formed crystals can be removed from magma, ending the chemical reactions between the magma and the minerals.

26 5.1 Section Check The presence of water decreases the melting temperature of rock. a. true b. false

27 5.1 Section Check Which component has the highest abundance in most of the magmas that form on Earth? a. iron b. potassium c. silica d. water

28 5.1 Section Check Crystals of plagioclase feldspar in an igneous rock are visibly zoned. Which explanation explains this observation? a. The crystals grew quickly. b. The crystals were partly dissolved. c. The magma had high gas content. d. The magma s composition changed.

30 5.2 Classification of Igneous Rocks Essential Questions What are the different types and textures of igneous rocks? How do cooling rates affect the grain sizes in igneous rocks? What are some of the uses of igneous rocks?

31 5.2 Classification of Igneous Rocks Classification of igneous rocks is based on mineral composition and texture. Review Vocabulary fractional crystallization: a sequential process during which early formed crystals are removed from the melt and do not react with the remaining magma

32 5.2 Classification of Igneous Rocks New Vocabulary intrusive rock extrusive rock basaltic rock granitic rock texture porphyritic texture vesicular texture pegmatite kimberlite

33 5.2 Classification of Igneous Rocks Mineral Composition of Igneous Rocks When magma cools and crystallizes below Earth s surface, intrusive rocks form. Magma that cools and crystallizes on Earth s surface forms extrusive rocks.

34 5.2 Classification of Igneous Rocks Mineral Composition of Igneous Rocks Igneous rocks are classified by their mineral compositions. Basaltic rocks, also called mafic rocks, are darkcolored, have lower silica contents, and contain mostly plagioclase and pyroxene.

35 5.2 Classification of Igneous Rocks Mineral Composition of Igneous Rocks Granitic rocks, also called felsic rocks, are lightcolored, have high silica contents, and contain mostly quartz and feldspar.

36 5.2 Classification of Igneous Rocks Mineral Composition of Igneous Rocks Rocks that have a composition of minerals that is somewhere between basaltic and granitic are called intermediate rocks. A fourth category, called ultrabasic, or ultramafic, contains rocks with only iron-rich minerals such as olivine and pyroxene and are always dark.

37 5.2 Classification of Igneous Rocks Mineral Composition of Igneous Rocks Rock type can be determined by estimating relative percentages of minerals in the rocks.

38 5.2 Classification of Igneous Rocks Texture Texture refers to the size, shape, and distribution of the crystals or grains that make up a rock.

39 5.2 Classification of Igneous Rocks Texture Crystal size and cooling rates When lava flows on Earth s surface, it cools quickly and there is not enough time for large crystals to form. The resulting extrusive igneous rocks have crystals so small that they cannot be seen without magnification.

40 5.2 Classification of Igneous Rocks Texture Crystal size and cooling rates When lava cools so quickly that crystals do not form, volcanic glass is the result. When magma cools slowly below Earth s surface, there is sufficient time for large crystals to form. Thus, intrusive rocks can have crystals larger than 1 cm.

41 5.2 Classification of Igneous Rocks Texture Porphyritic rocks A porphyritic texture is characterized by large, well-formed crystals surrounded by finer-grained crystals of the same mineral or different minerals.

42 5.2 Classification of Igneous Rocks Texture Vesicular rocks The spongy appearance that results from gas bubbles trapped in lava is called vesicular texture.

43 5.2 Classification of Igneous Rocks Thin Sections Scientists use a special microscope, called a petrographic microscope, to help them identify minerals by examining the mineral grains in sections of rock thin enough for light to pass through.

44 5.2 Classification of Igneous Rocks Igneous Rocks as Resources Veins Valuable ore deposits often occur within igneous intrusions. At other times, they may occur as veins in the rocks surrounding intrusions.

45 5.2 Classification of Igneous Rocks Igneous Rocks as Resources Pegmatites Veins of extremely large-grained minerals that can contain ores are called pegmatites.

46 5.2 Classification of Igneous Rocks Igneous Rocks as Resources Kimberlites Diamonds and other minerals that can form only under very high pressure are found in rare, ultrabasic rocks known as kimberlites.

47 5.2 Classification of Igneous Rocks Igneous Rocks as Resources Igneous rocks in construction The interlocking grain textures and the resistance to weathering of many of the minerals present in igneous rocks make them especially useful as building materials.

48 5.2 Section Check Which rock is the intrusive equivalent of basalt? a. granite b. diorite c. gabbro d. obsidian

49 5.2 Section Check In which igneous rock should a person prospect for diamonds? a. granite b. kimberlite c. basalt d. pegmatite

50 5.2 Section Check What information about an igneous rock might a person learn from a description of its texture? Answer: A description of the texture of an igneous rock may provide information about the depths at which a rock was formed, and how quickly the magma cooled.

52 CHAPTER 5 Igneous Rocks Resources Earth Science Online Study Guide Chapter Assessment Questions Standardized Test Practice Click on a hyperlink to view the corresponding feature.

53 5.1 What are igneous rocks? Study Guide Igneous rocks are the rocks that form when molten material cools and crystallizes. Magma consists of molten rock, dissolved gases, and mineral crystals. Magma is classified as basaltic, andesitic, or rhyolitic, based on the amount of silica it contains.

54 5.1 What are igneous rocks? Study Guide Different minerals melt and crystallize at different temperatures. Bowen s reaction series defines the order in which minerals crystallize from magma.

55 5.2 Classification of Igneous Rocks Study Guide Classification of igneous rocks is based on mineral composition and texture. Igneous rocks are either ultrabasic, basaltic, intermediate, or granitic. The rate of cooling determines crystal size.

56 5.2 Classification of Igneous Rocks Study Guide Ores often occur in pegmatites. Diamonds occur in kimberlites. Some igneous rocks are used as building materials because of their strength, durability, and beauty.

57 CHAPTER 5 Igneous Rocks Chapter Assessment According to Bowen s reaction series, which mineral crystallizes at the highest temperature? a. olivine b. amphibole c. quartz d. potassium feldspar

58 CHAPTER 5 Igneous Rocks Chapter Assessment Which texture indicates that an igneous rock cooled very quickly? a. vesicular b. coarse-grained c. glassy d. spongy

59 CHAPTER 5 Igneous Rocks Chapter Assessment A student is examining thin sections of a gabbro and a granite. Which mineral should the student identify in the gabbro but probably not identify in the granite? a. quartz b. potassium feldspar c. muscovite mica d. olivine

60 CHAPTER 5 Igneous Rocks Chapter Assessment Magmas of several different compositions have erupted from the same volcano. How can this be explained by the concept of fractional crystallization?

61 CHAPTER 5 Igneous Rocks Chapter Assessment Answer: Fractional crystallization is one way that different magmas can be produced at the same volcano. If magma is injected beneath the volcano and begins to crystallize, the composition of the remaining magma will change as the crystals form. The magma may then erupt from the volcano at any time.

62 CHAPTER 5 Igneous Rocks Chapter Assessment Why are igneous rocks sometimes used as building stones? Answer: Igneous rocks are hard and often durable. They can endure the outdoor environment on buildings or in statues. Many igneous rocks consist of crystals that have attractive colors, shapes, and arrangements. When cut and polished, these rocks make attractive floors, walls, and countertops.

63 CHAPTER 5 Igneous Rocks Standardized Test Practice An igneous rock consists entirely of olivine. Which composition does the rock have? a. granitic b. intermediate c. basaltic d. ultrabasic

64 CHAPTER 5 Igneous Rocks Standardized Test Practice The igneous rock pumice has many holes. What do these holes represent? a. dissolved crystals b. gas pockets c. pores between grains d. fractures in the rock

65 CHAPTER 5 Igneous Rocks Standardized Test Practice The graph shows Earth s geothermal gradient. In which of the following depth ranges does temperature increase most rapidly? a. 0 to 1000 meters b to 2000 meters c to 4000 meters d to 5000 meters

66 CHAPTER 5 Igneous Rocks Standardized Test Practice Which rock formed from lava that cooled on Earth s surface? a. rhyolite b. granite c. diorite d. gabbro

67 CHAPTER 5 Igneous Rocks Standardized Test Practice Hot, water-rich fluids sometimes form during the last stages of magma crystallization. Why are these fluids important?

68 CHAPTER 5 Igneous Rocks Standardized Test Practice Answer: The fluids often include rare and valuable elements that have very low concentrations in Earth s crust as a whole. Watery fluids sometimes form metal-rich veins or other metal-rich deposits that include these valuable elements.

IGNEOUS ROCKS. SECTION 5.1 What are igneous rocks?

IGNEOUS ROCKS. SECTION 5.1 What are igneous rocks? Date Period Name IGNEOUS ROCKS SECTION.1 What are igneous rocks? In your textbook, read about the nature of igneous rocks. Use each of the terms below just once to complete the following statements. basaltic