1. Lab ONLINE LESSON
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2. DO TAKE NOTES WHILE PERUSING ALONG…

3. Lab 05
Igneous Rocks

4. But first, what is a rock?

5. A rock is a collection of minerals…

6. There’s a mineral
There’s a mineral
There’s a mineral

7. As you may recall, a mineral is…

8. 1. An inorganic compound....formed through physical forces and not biological forces

9. 2. A naturally occurring object...

10. Has a specific chemical composition...eg…
CaCO3
Fe2O3

11. 4. A distinctive set of physical properties...
hardness, streak, luster etc. etc. etc...

12. 5. And has a crystalline structure
5. And has a crystalline structure... with a 3 dimensional arrangement of atoms

13. 6. And is a solid…no liquids or gas…

14. So a rock is just a collection of minerals

15. The Rock Cycle can be used to illustrate the life of rocks…

16. Igneous rocks start out as a melt below the surface of our planet…this is magma

17. Magma can be pushed up to the surface where it is called lava…

18. Magma and lava can solidify in place to form plutonic and volcanic rocks…

19. Eventually, igneous rocks break apart to form sediment…

20. Sediment then can bind together to sedimentary rocks…

21. Sedimentary rocks can then be reprocessed by applying changes in temperature and pressure to form metamorphic rocks…

22. Enough changes in pressure and temperature, rocks can then re-melt back to igneous rocks…then the whole process starts again…

23. This is The Rock Cycle…

24. There are three rock groups…

25. AC/DC
Metallica
Led Zeppelin

26. Ha ha ha ha…that was supposed to be funny…ha ha ha ha ha hah ho hoho…uh

27. Was it funny?

28. Somebody say yes.

29. Good

30. The three rock groups are…

31. Igneous
Sedimentary
Metamorphic

32. Igneous rocks will be our focus today…

33. are produced from a melt
Igneous Rocks
are produced from a melt

34. Igneous rocks start out as a melt (liquid rock) below the surface of the earth. This is called magma….

35. Eventually, this magma pushes up to the surface and becomes lava

36. Lava and magma are chemically the same just one is below ground and the other is above…

37. Igneous rocks that form below ground are called plutonic rocks

38. Igneous rocks that form above ground are called volcanic rocks…

39. Igneous rocks that form below ground are also called intrusive rocks and igneous rocks that form above ground can be called extrusive rocks…

40. Volcanic/Extrusive
Plutonic/Intrusive
Plutonic/Intrusive = below ground
Volcanic/Extrusive = above ground

41. Both magma and lava cool to form crystals of minerals…a rock is a collection of minerals

42. Press the play button to see magma in action

43. Now that we know a little about the source material for igneous rocks…let’s take a look at some characteristics…

44. To identify igneous rocks…we need to look at
Texture Mineral content 3.Gases

45. Texture of igneous rocks refers to the crystal size…

46. Crystal size is determined by the rate of cooling of magma or lava…

47. Rate of cooling Fast Cooling Slow Cooling Aphanitic Texture
Phaneritic Texture

48. A fast cooling magma produces small crystals
Or an aphanitic texture

49. This rock possesses aphanitic crystals…

50. A slow cooling magma produces large crystals
Or an phaneritic texture

51. Aphanitic igneous rocks form in a volcanic environment…or above ground…

52. This rock possesses phaneritic crystals…

53. Aphanitic crystals cannot be seen with the naked eye…they are too small…

54. Phaneretic igneous rocks form in a plutonic environment…or below ground…

55. Phaneretic crystals can be seen with the naked eye…

57. Another texture is called porphyritic… this is a collection of large and small crystals…

58. This is caused by originally slow cooling then an episode of fast cooling…

59. Producing a rock with various sized crystals…

60. So texture is based upon crystal size which is dependant upon the
environment of formation…

61. 2. Mineral content is the proportion of minerals in an igneous rock…

62. There are 8 minerals that make up most igneous rocks…

63. 1.Quartz 2.plagioclase feldspar 3. potassium feldspar 4. muscovite

64. These are FELSIC minerals because of their light coloration
These are FELSIC minerals because of their light coloration. Grays, whites and pink…

65. FELSIC minerals are predominantly silica or quartz rich…

66. 5. Biotite 6. Pyroxene 7. Olivene 8. Amphibole

67. These are MAFIC minerals because of their dark coloration
These are MAFIC minerals because of their dark coloration. Dark grays, green and black…

68. MAFIC minerals are also called ferromagnesian minerals…they are rich in iron and magnesium…

69. Igneous rocks can be identified by their mineral content and texture…

70. Igneous rocks are identified by their MAFIC or FELSIC mineral content…

71. This chart from your lab manual illustrates how mineral
content is used to identify igneous rocks

72. The identification of igneous rocks is just a contest between MAFIC and FELSIC minerals…

73. So in general, if a rock posesses 0% to 15% MAFIC minerals, then it plots in this range

74. If a rock posesses 45% to 85% MAFIC minerals, then it plots in this range…

75. GRANITE is also an intrusive and plutonic rock…
If an igneous rock is rich in quartz, and feldspar and posesses a phaneritic texture, then it is called GRANITE…it is also a FELSIC igneous rock…
GRANITE is also an intrusive and plutonic rock…

76. BASALT is also an extrusive and volcanic rock
If an igneous rock is rich in augite and plagioclase feldspar, and posesses an aphanitic texture, then it is called BASALT…it is also a MAFIC igneous rock…
BASALT is also an extrusive and volcanic rock

77. The significance of FELSIC vs MAFIC rocks can be seen in the chart below

78. This chart is referred to as Bowen’s Reaction Series…

79. MAFICs are high temperature rocks…eg olivene and pyroxene…

80. FELSICs are low temperature rocks…eg quartz, K-feldspar and muscovite…

81. Mineral content is an indicator of the temperature environment in which igneous rocks form…

82. 3. Gases are used in the identification of igenous rocks…

83. Melted rocks contain volatiles such as water and carbon dioxide…

84. As melted rocks reach the surface of the earth, gases are released producing bubbles that solidfy

85. Pumice is a very good example of escaping gases…

86. There are a lot of openings where gases escaped…

87. These openings are called vesicles…

88. Vesicles appear only in volcanic, extrusive, aphanitic igneous rocks……

89. Vesicles do not appear in plutonic, intrusive rocks…

90. It is now time for a short quiz….ask Bob for a worksheet…