1. Records of Geologic Past
Rocks Tell Stories
Records of Geologic Past

2. Rock Classification – 3 major groups based on their methods of formation or origin
Igneous rocks … from cooling and solidification of lava or magma
Sedimentary rocks … from compacted and cemented sediments, or chemical precipitates or evaporites
Metamorphic rocks … meta (change) morphic (form) … rocks changed by heat and pressure –but remain solid

4. IGNEOUS ROCKS

5. Formation of Igneous Rocks
COOLING AND SOLIDIFICATION OF MAGMA/LAVA
INTERGROWN OR INTERCONNECTED SILICATE CRYSTALS IN A RANDOM PATTERN – NOT ORGANIZED

6. INTERGROWN SILICATE CRYSTALS - RANDOM PATTERN

8. MAGMA VS. LAVA Magma – molten material BELOW the surface of the Earth
Lava – molten material AT OR ABOVE earth’s surface

9. ENVIRONMENT OF FORMATION
COOLING HISTORY
MAGMA
LAVA
Intrusive – below the surface
Extrusive - above the surface
A pluton is a body or chamber of magma deep inside the crust.
Ejected from volcano
Rocks formed when magma cools and solidifies are called
INTRUSIVE (PLUTONIC)
Rocks formed when lava cools and solidifies are called
EXTRUSIVE (VOLCANIC)

10. IGNEOUS ROCKS ARE CLASSIFIED BASED ON 2 MAIN CHARACTERISTICS
TEXTURE – MINERAL GRAIN SIZE
MINERAL COMPOSITION (COLOR)

11. Classification of Igneous Rocks by Texture
WHAT IS TEXTURE?
It is NOT how it feels!
It’s the SIZE OF MINERAL CRYSTALS

12. How fast an igneous rock cools.
What controls texture?
How fast an igneous rock cools.
What controls how fast an igneous rock cools?
Where the rock is formed.
slower cooling
coarser crystals
deep in ground

13. ESRT – TOP OF THE IGNEOUS ROCK SCHEME TELLS THE
TEXTURE / GRAIN SIZE

14. Classification of Igneous Rocks – Texture or Grain Size
Extrusive
Intrusive
Volcanic - LAVA
Volcanic- LAVA
Plutonic - MAGMA
Extremely fast cooling
Fast Cooling
Slow
Cooling
Extremely slow cooling
Non-crystalline
Glassy vesicular (gas pockets)
Fine-grained
Coarse-grained
Very Coarse-grained

15. EXTRUSIVE – VOLCANIC - LAVA
When lava cools extremely fast crystals have no time to form – JUST FROZEN IN PLACE RANDOMLY WHEN LAVA ENTERS ATMOSPHERE OR WATER
GLASSY – NON-CRYSTALLINE
Non-vesicular Vesicular
gas pockets

16. EXTRUSIVE – VOLCANIC - LAVA
Lava that cools fast at or near the
Earth’s surface
Produces small crystals
FINE-GRAINED TEXTURE
not easily seen with the naked eye.

17. INTRUSIVE – PLUTONIC - MAGMA
Magma that cools slowly deep underground
produces large crystals
COARSE-GRAINED TEXTURE
easily seen with the naked eye.

18. INTRUSIVE – PLUTONIC - MAGMA
EXTREMELY SLOW COOLING HAS ABNORMALLY LARGE CRYSTALS AND IS VERY COARSE.  

19. CHARACTERISTICS OF IGNEOUS ROCKS
IN THE MIDDLE OF THE IGNEOUS ROCK CHART ARE CHARACTERISTICS BASED ON WHICH MINERALS ARE IN EACH ROCK.
NOTICE 2 NEW WORDS
FELSIC AND MAFIC

20. FELSIC VS. MAFIC FELSIC MAFIC “FEL” = FELDSPARS “MA” = MAGNESIUM
“SIC” = SILICA
“F” = IRON
High % of quartz, feldspars, mica
“IC” = SILICA
High % of pyroxene, feldspars, amphibole
LIGHTER IN COLOR LESS DENSE
DARKER IN COLOR
MORE DENSE

21. Continental mixed oceanic mantle
FELSIC MAFIC ULTRAMAFIC

22. THE BOTTOM OF THE IGNEOUS ROCK SCHEME TELLS YOU THE COMPOSITION
TEXTURE + COMPOSITION CAN NAME ROCK

23. FELSIC COMPOSITION COLUMN+
COARSE TEXTURE ROW

24. Granite Rhyolite Figure 4.7 A INTRUSIVE EXTRUSIVE
MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive

25. Andesite Diorite Figure 4.7 B INTRUSIVE EXTRUSIVE
MINERAL COMPOSITION THE SAME ---- TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive
Diorite
Figure 4.7 B

26. Basalt Gabbro INTRUSIVE EXTRUSIVE
MINERAL COMPOSITION THE SAME – TEXTURE ONLY DIFFERENCE
Intrusive vs. Extrusive

27. WHAT GRAPH BELOW SHOWS AS TIME INCREASES THE SIZE INCREASES?

28. SEDIMENTARY ROCKS

30. Sedimentary Rocks
80 % of Earth’s surface is covered with sediments and Sedimentary Rocks (only a thin layer on top)

32. What is sediment???? Broken pieces of rocks called Sediments
Chemical precipitates ( dissolved solids come out of solution)
Organic fragments – shells, decayed plant matter – this is called BIOCLASTIC

33. Source of Sediment
When Igneous, Metamorphic Rocks, and Sedimentary Rocks are uncovered and exposed to the atmosphere and hydrosphere they start to break down
Weathering is the general term for all actions that break down or wear away rock
Erosion is the moving/transport of the sediment

34. Sedimentary Rocks form when sediments are transported to large bodies of water and are …
Deposited in horizontal layers called beds or strata
Buried
Compacted – particles forced extremely close together because of the pressure of the overlying layers and water
Cemented – glued together

35. Sedimentary Rocks
Sediments that are eroded settle to the bottom of the rivers, lakes, and oceans
Layer after layer of eroded earth is deposited on top of each other

37. Most Sedimentary Rocks form under large bodies of water, such as lakes, seas, and oceans

38. Horizontal layers deposited under water

39. Classification of Sedimentary Rocks
We classify sedimentary rocks depending whether the sediments are
LAND DERIVED (came from)
CHEMICALLY - ORGANICALLY DERIVED

41. INORGANIC LAND DERIVED ROCKS NAMED BY GRAIN SIZE

42. Sediments are pebbles, cobbles, and boulders
rounded
Breccia
angular

43. Silt (0.006 to cms.
SILTSTONE
Sand (0.2 to cms.)
SANDSTONE
Clay (less than cms.)
SHALE

45. 2 TYPES OF TEXTURE CRYSTALLINE FOR CHEMICALLY FORMED SEDIMENTARY ROCKS
BIOCLASTIC FOR ORGANICALLY FORMED SEDIMENTARY ROCKS
HOW USEFUL IS GRAIN SIZE????

47. CHEMICAL Sedimentary Rocks Sediment From Solution
All liquid water contains dissolved minerals.
These minerals precipitate (dissolved solids come out of solution/water)
Usually happens because of evaporation

48. Characteristics of Chemically Formed Sedimentary Rocks
They are monominerallic – consisting of intergrown crystals of just 1 mineral.
Form in shallow seas

50. ROCK SALT
Intergrown crystals of just 1 mineral
DOLOSTONE
ROCK GYPSUM

52. ORGANIC Sedimentary Rocks Bioclastic Sediment
LIMESTONE AND CORALS
Dissolved minerals taken out of solution by marine organisms for their hard parts (shells) can pile up on the seafloor when they die.
These fossil remains accumulate into a thick enough layer to form an “organic” sedimentary rock
Cement is commonly calcite ( bubbles with acid)
COAL
Decayed plant remains

53. CHEMICALLY PRECIPITATED LIMESTONE
BIOCLASTIC LIMESTONE
COAL

54. Summary
Inorganic Land-Derived Sedimentary Rocks are identified by Texture or Grain Size
Chemically and/or Organically Formed Sedimentary Rocks are identified by Composition

55. HIGH ENERGY
LOW ENERGY

56. Environment of Formation Ocean Derived Sedimentary Rocks
help us understand our past
geologic history
There is evidence of climate
change as well as lost species
of plants and animals in

57. During the Cretaceous Period (about 120 mya) a shallow inland sea split North America.
We know this by the Sedimentary Rocks deposited in the former shallow sea
KANSAS AND KENTUCKY HAVE A GREAT DEAL OF CHALK – TELLS ME ONCE UNDERWATER
WHITE CLIFFS OF DOVER – ENGLAND UNDER WATER
DURING CRETACEOUS PERIOD 120 MYA, LATIN FOR CHALK – A GREAT DEAL OF CHALK WAS FORMED DURING THIS PERIOD. CLIMATE WAS VERY MILD, ICE FREE POLAR REGIONS
1/3 OF NORTH AMERICA WAS FLOODED – NO MODERN GULF OF MEXICO

58. New York's salt deposits occur layered with shale, dolomite, and anhydrite in the lower part of the Silurian-aged Salina group. The Salina group outcrops in an east-west band from near Buffalo and Rochester through Syracuse to Herkimer County. At the southern edge of the state the salt is 3,000 feet deep.

59. SALT AND GYPSUM EVAPORATION
Bedrock of Salt and Gypsum around Buffalo
What type of environment would cause salt and/or gypsum to evaporate?
Ocean environment with hot temperatures
KANSAS AND KENTUCKY HAVE A GREAT DEAL OF CHALK – TELLS ME ONCE UNDERWATER
WHITE CLIFFS OF DOVER – ENGLAND UNDER WATER
DURING CRETACEOUS PERIOD 120 MYA, LATIN FOR CHALK – A GREAT DEAL OF CHALK WAS FORMED DURING THIS PERIOD. CLIMATE WAS VERY MILD, ICE FREE POLAR REGIONS
1/3 OF NORTH AMERICA WAS FLOODED – NO MODERN GULF OF MEXICO

60. CHARACTERISTICS OF SEDIMENTARY ROCKS
Horizontal layers called beds or strata
Clasts are rounded and sorted because they have been moved by water
Ripple Marks
Mud Cracks
Fossils
Interconnected mineral crystals of 1 mineral (monominerallic)

61. HORIZONTAL LAYERS

62. A. SHALLOW WATER B. LOW ENERGY C. DIRECTION OF FLOW

63. MUDCRACKS
ALTERNATING WET AND DRY CONDITIONS

64. Limestone - FOSSILS

65. SEDIMENTARY ROCK MANTRA
COMPACTED AND CEMENTED SEDIMENTS
FOSSILS
RIPPLE MARKS
MUDCRACKS

66. METAMORPHIC ROCKS

68. METAMORPHIC ROCKS META = CHANGE MORPH = FORM
Start with pre-existing rock and change to another rock – but these changes occur in the SOLID STATE
Change occurs because the rock is moved into an environment in which the minerals which make up the rock become unstable and out of equilibrium with the new environmental conditions
In most cases, this involves BURIAL which leads to a rise in temperature and pressure

69. METAMORPHISM
Process by which igneous, sedimentary, or another metamorphic rock called the “parent rock” undergoes changes in minerals and texture

70. Occurs in rocks due to the effects of
METAMORPHISM
Occurs in rocks due to the effects of
High temperature
High pressure

71. HEAT EFFECTS
Temperature increases with depth or contact with magma
Recrystallization – a process that forms new mineral crystals because the mineral is no longer stable at the new temperature
Changes to a new (high temperature) mineral

72. PRESSURE EFFECTS Mineral crystals grow larger
Pressure increases with depth – weight of overlying rock (see page 10 ESRT)
Mineral crystals grow larger
Mineral crystals are more dense
Mineral crystals grow perpendicular to pressure
Mineral crystals are arranged in parallel layers – PRODUCES FOLIATION

73. FOLIATION
Pressure actually rearranges the minerals into parallel layers.
More pressure – minerals grow larger and recrystallize and separate into layers
Even more pressure – alternating layers of light and dark minerals called
Banding

75. Random arrangement of minerals
Organized arrangement of minerals - banding

76. METAMORPHIC ROCK MANTRA
INTERGROWN CRYSTALS IN AN ORGANIZED PATTERN

77. Granite
Intergrown crystals
random pattern
Gneiss
Intergrown crystals
Organized Pattern

78. 2 Types of Metamorphism
Regional Metamorphism – Occurs over large areas where there is active mountain building
Convergent plate boundaries
Contact Metamorphism – areas in contact with magma intrusions and/or lava extrusions

80. MOUNTAIN
BUILDING
Let’s start with regional metamorphism

81. Classification of Regional Metamorphic Rocks
Composition is basically the same for all foliated rocks – parent rock is usually listed in comments section.
Type of texture and grain size determined by the amount of heat and pressure

83. GRADES OF METAMORPHISM
LOW GRADE – LESS HEAT AND PRESSURE – SLATE
HIGH GRADE – MORE HEAT AND PRESSURE - GNEISS

84. Temperature Low-grade metamorphism:
Occurs at about 2000 C to 5000 C. and pressure greater than 1,000 atmospheres
High-grade metamorphism:
Occurs at > 5000 C

85. FOLIATED METAMORPHIC ROCKS

86. MICA SCHIST WITH GARNET
MICA CRYSTALS
BECOME
LARGE AND SPANGLY

87. METAMORPHIC ROCKS WILL OFTEN BE DEFORMED BECAUSE OF INTENSE HEAT AND PRESSURE
LOOK AT ROCK SYMBOL FOR GNEISS

88. DEFORMED GNEISS

89. A metamorphic rock exposed to too much heat will melt and become ???
MAGMA

90. CONTACT METAMORPHISM

91. Contact Metamorphic Metamorphism means "changed form".
The Changes occur because of:
Heat from magma intruding on the surrounding rock
Very little pressure

92. Near magma chambers (plutons)
Rocks in “contact” with the magma are heated
New minerals are formed –recrystallization

93. Contact Metamorphism – heating the adjacent rocks

94. Symbol for Contact Metamorphism is a line with tick marks
When limestone undergoes contact metamorphism what rock will it metamorphose into? Sandstone??

95. PARENT ROCK IN THE COMMENTS

96. LIMESTONE METAMORPHOSES INTO MARBLE

97. SANDSTONE METAMORPHOSES INTO QUARTZITE