1. The three major categories of rocks

2. The Rock Forming minerals The most abundant minerals in the earth’s crust and the most common in rocks are:- Quartz Feldspar Mica Pyroxene

3. Igneous Rocks Formed by the cooling and solidification of melted rock (molten silicate liquid) called magma or lava.

7. Classification of igneous rocks Texture – crystal size All large crystals - Produced by relatively slow cooling deep underground. - Found in intrusive igneous rocks.

8. Classification of igneous rocks Crystal size -Small crystals and/or glass -Produced by rapid cooling, usually at or near the earth’s surface. Typical of extrusive rocks. Occasionally in intrusive rocks close to the surface.

10. Classification of igneous rocks Other textures Bubbles which are trapped in igneous rocks are called vesicles. E.g Pumice. Broken fragments If there is enough gas, expanding bubbles cause lava to break into fragments explosively. E.g. volcanic ash and pumice.

13. Sediments and Sedimentary rock There are different types of sediment 1.Clastic sediments (also called detrital sediment). 2.Chemical sediment 3.Biochemical sediment

14. Some examples

15. Textures of Sedimentary rock Clastic sediment Maximum grain size – fine, medium and coarse. Grain shape – angular and rounded. Sorting – well or poorly sorted.

16. Well and poorly sorted sediment

17. Clastic rocks By texture Course and rounded – conglomerate Course and angular – breccia Medium - sandstone Fine – siltstone, mudstone, claystone or shale.

19. Sandstone by composition Pure quartz sand – quartz sandstone Sand and fine matrix – graywacke sandstone. Sand with 20% rock fragments – lithic sandstone.

21. Chemical and biochemical Sedimentary Rocks Calcite – Limestone Plant remains – Coal or peat Silica – Chert Halite – Rock Salt Gypsum – Rock Gypsum

24. Sedimentary structures Layering Ripples Cross-bedding Mud craks Burrows and tracks (fossils)

28. Metamorphism Includes process which change the minerals and texture of rock without melting it

29. Causes of metamorphism Pressure Different minerals are stable at different pressures. Changing the pressure can change the types of minerals in rocks.

30. Causes of metamorphism Temperature Different minerals are stable at different temperatures. Changing the temperature can cause the types of minerals present in the rock to change.

31. Causes of metamorphism Hydorthermal fluids Usually water and/or CO2 plus dissolved materials. Can change the chemical composition of rocks by adding or removing materials. Many important ore deposits have been formed by metamorphic deposits.

33. Other types of metamorphism Deformation – along fault lines Hydrothermal – associated with igneous intrusions along ocean ridges Burial – caused by deep burial. Shock – caused by sudden high pressures caused during impacts

35. Metamorphic rocks Composition and texture are used to decribe these rocks, just like the previous ones.

36. Metamorphic rocks Texture Foliated rocks and this refers to the preferred orientation of the mineral grains in rocks as a result of directed pressure. Non-foliated rocks have no mineral orientation.

38. Foliated metamorphic rocks Slate Schist Gneiss Phyllite

41. Non-foliated metamorphic rocks Quartzite Marble Skarn Hornfels

45. Sedimentary Rocks Metamorphic Rocks The Rock Cycle Sediments Magma

46. Sediments Sedimentary Rock Metamorphic Rock Igneous Rock Magma Cooling Melting Heat and pressure Uplift Heat and pressure Burial and lithification Deposition in oceans and on continents Weathering and erosion

48. Minerals Make up the lithosphere, mantle and the core. Over 4000 are known. Minerals are used extensively by humans. Minerals record information about the processes that formed them.

51. Minerals the building blocks of rocks Definition of a mineral. Homogenous (uniform throughout) Naturally occurring (no synthetics) Inorganic (no biological stuff) Solid (no liquid or gas) Ordered internal molecular structure Definite chemical composition

52. Rocks An aggregate of minerals Most rocks have more than one Mineral. Some rocks are mono mineralic

53. Granite is an igneous rock made up of several minerals QuartzFeldsparHornblende

54. Crystals A single continuous mineral with crystal faces. The faces indicate growth in an open space. Crystals of the same minerals have similar faces, which reflect the ordered atomic arrangement.

55. Polymorphs These are minerals with the same chemical composition. But different crystalline structures Diamond and graphite are polymorphs of (C).

58. Mineral Physical Properties The characteristics determined by your 5 senses. Used to ID minerals Depend upon… Chemical Composition Crystal Structure

59. Physical Properties Crystal Form Crystal Habit Luster Color Streak Hardness Cleavage Fracture Specific Gravity

60. Crystal Form Ideal shape displayed by crystal faces. These are variable and depend on the chemicals involved.

61. Crystal Form Minerals may exhibit a range of crystal face development Euhedral – Well-developed Anhedral – No visible crystal faces. Usually from growth in a confined space. Subhedral – Between the two.

62. Crystal Form Crystals need an open space to grow, or they take on a different form. Quartz crystals from an open and closed space.

63. Luster Appearance in reflected light. Two categories Metallic Non-metallic Vitreous (glassy) Silky Resinous Earthy (dull) Adamantine (brilliant)

64. Colour Often unreliable for mineral ID. May vary due to impurity elements. Many gemstones are brightly colored.

65. Streak Color of a mineral when scratched (crushed) on an unglazed porcelain plate.

66. Hardness Resistance of a mineral to abrasion or scratching. All minerals are compared to a standard scale called the Mohs scale of hardness.

67. Moh’s scale of hardness 10Diamond 9Corundum 8Topaz 7Quartz 6Feldspar 5ApatiteGlass 4Flourite 3CalciteCoin 2GypsumFingernail 1Talc Hardest Softest

68. Cleavage Tendency to break along planes of lattice weakness. Cleavage produces flat, shiny surfaces. Described by resulting geometric shapes. Number of planes Angles between adjacent planes Be careful to discriminate from crystal form

69. Cleavage Cleavage in one direction

70. More Cleavage 2 directions at 90º 2 directions NOT at 90º Example: Amphibole Example: Potassium Feldspar Cleavage

71. More Cleavage 3 directions at 90º 2 directions NOT at 90º

72. Conchoidal Fracture Some minerals lack planes of weakness. Molecular bonds are equally strong in all directions. They don’t cleave; they fracture. Conchoidal fracture - curved surfaces, sharp edges.

73. Specific Gravity Ratio of the weight of a mineral to the weight of an equal volume of water Average crustal value is 2.7 (quartz) Average mantle value is 3.3 (olivine) SG is reflected in “heft” – how heavy the mineral feels. Galena – Heavy Feldspar - Light