1. Chapter 20: ROCKS AND MINERALS.
Chapter 20:
ROCKS AND MINERALS

2. This lecture will help you understand:
The Geosphere is Made Up of Rocks and Minerals
Minerals
Mineral Properties
Classification of Rock-Forming Minerals
The Formation of Minerals and Rock
Rock Types
Igneous Rocks
Sedimentary Rocks
Metamorphic Rocks
The Rock Cycle

3. The Geosphere is Made Up of Rocks and Minerals
Just eight elements account for 98% of Earth’s mass.
Figure 20.2 CPS4

4. The Geosphere is Made Up of Rocks and Minerals
From Earth’s early molten (or nearly molten) state under the influence of gravity, the heaviest elements sank to the center of the Earth. So the core is composed of dense, iron-rich material.
Lighter elements migrated toward Earth’s surface. So the mantle is less dense than the core.
The crust is composed of even lighter, silicon- and oxygen-rich material.
Figure 20.3 CPS4

5. The Geosphere is Made Up of Rocks and Minerals
Oxygen and silicon make up 75% of Earth’s crust.

6. Minerals
They are naturally occurring (formed naturally rather than manufactured).
They are crystalline solids.
They have an orderly and repeating arrangement of atoms, ions, and or molecules.
They have a definite chemical composition, with slight variations.
They are generally inorganic.

7. Minerals Minerals are classified by: Chemical composition
Crystal structure

8. Minerals
Crystallization is the formation and growth of a solid from a liquid or gas
Atoms come together in specific chemical compositions and geometric arrangements.
The combination of chemical composition and arrangement of atoms in an internal structure makes each mineral unique.
Many minerals are identifiable by their crystal form.

9. Minerals
Some minerals can have the same composition but have a different crystal structure.
Different arrangements of the same atoms result in different minerals.
Diamond and graphite are two examples
Such minerals are called polymorphs.
With a different crystal structure, the minerals will have different properties.

10. Mineral Properties
Physical properties are an expression of chemical composition and internal crystal structure:
Crystal form
Hardness
Cleavage and fracture
Color
Density

11. Mineral Properties: Crystal Form
Crystal form—crystal shape—is the outward expression of a mineral’s internal arrangement of atoms.
Internal atomic arrangement is determined by atom/ion charge, size, and packing.
The conditions in which the crystal grows also affect crystal form.
Temperature, pressure, space for growth
Well-formed minerals are rare in nature—most minerals grow in cramped confined spaces.

12. Mineral Properties: Hardness
Hardness is the resistance of a mineral to scratching.
Hardness is dependent on the strength of a mineral’s chemical bonds.
Bond strength is determined by ionic charge, atom (or ion) size, and packing.
The Mohs Scale compares the hardness of different minerals.

13. Gold is a soft mineral because:
Mineral Properties: Hardness
CHECK YOUR NEIGHBOR
Gold is a soft mineral because:
Its atoms are very tightly packed.
Its atoms are large.
Its atoms are tightly bonded.
It has a very high melting point.
B) Its atoms are large.

14. Gold is a soft mineral because:
Mineral Properties: Hardness
CHECK YOUR ANSWER
Gold is a soft mineral because:
Its atoms are very tightly packed.
Its atoms are large.
Its atoms are tightly bonded.
It has a very high melting point.
B) Its atoms are large.

15. Mineral Propteries: Cleavage and Fracture
Cleavage is the property of a mineral to break along planes of weakness.
Planes of weakness are determined by crystal structure and bond strength.
Fracture occurs in minerals where bond strength is generally the same in all directions.
Minerals that fracture do not exhibit cleavage.

16. Mineral Properties: Color
Color is an obvious feature for many minerals, but it is not reliable for mineral identification.
Chemical impurities can change a mineral’s color.
A mineral may occur in many color variations or be colorless.

17. Mineral Properties: Density
Density is the ratio of a mineral’s mass to its volume.
In simple terms, it is how heavy a mineral feels for its size (volume).

18. Physical properties of a mineral are predominantly related to
Mineral Properties
CHECK YOUR NEIGHBOR
Physical properties of a mineral are predominantly related to
the external conditions of temperature, pressure, and amount of space available for growth.
the chemical composition and the internal arrangement of the atoms that make up the mineral.
crystal form, hardness, cleavage and fracture, and density.
all of the above.
B) The chemical composition and the internal arrangement of the atoms that make up the mineral.

19. Physical properties of a mineral are predominantly related to
Mineral Properties
CHECK YOUR ANSWER
Physical properties of a mineral are predominantly related to
the external conditions of temperature, pressure, and amount of space available for growth.
the chemical composition and the internal arrangement of the atoms that make up the mineral.
crystal form, hardness, cleavage and fracture, and density.
all of the above
B) The chemical composition and the internal arrangement of the atoms that make up the mineral.

20. The color of a mineral is predominantly related to
Mineral Properties
CHECK YOUR NEIGHBOR
The color of a mineral is predominantly related to
its chemical composition.
its internal arrangement of atoms.
its luster.
temperature and pressure conditions at the time of crystallization.
A) Its chemical composition.

21. The color of a mineral is predominantly related to
Mineral Properties
CHECK YOUR ANSWER
The color of a mineral is predominantly related to
its chemical composition.
its internal arrangement of atoms.
its luster.
temperature and pressure conditions at the time of crystallization.
Its chemical composition.
Although atomic arrangement and chemical composition determine color, slight changes in chemical composition can change a mineral’s color. Quartz is found in shades of pink (rose quartz), cloudy white (milky quartz), black (smoky quartz), and purple (amethyst). Slight impurities in the mineral corundum (Al2O3) give us ruby (traces of Cr) and sapphire (traces of Fe or Ti).

22. Classification of Rock-Forming Minerals
There are two classifications of minerals:
Silicate minerals
Nonsilicate minerals
Silicate minerals make up more than 90% of the Earth’s crust.

23. Classification of Rock-Forming Minerals
Silicate minerals are made up of silicon (Si) and oxygen (O) atoms, along with other elements (Al, Mg, Fe, Mn, and Ti).

24. Classification of Rock-Forming Minerals
The Silicates are divided into two groups:
Ferromagnesian silicates
Contain iron and/or magnesium
Tend to have high density and are darkly colored
Nonferromagnesian silicates
No iron or magnesium
Tend to have low density and are light in color

25. Classification of Rock-Forming Minerals
All silicate minerals have the same fundamental structure of atoms—the silicate tetrahedron.

26. Classification of Rock-Forming Minerals
Nonsilicate minerals make up about 8% of Earth’s crust.
Carbonate minerals
Calcite, dolomite
Oxide minerals
Ore minerals—hematite, magnetite, chromite
Sulfide minerals
Ore minerals—pyrite, galena
Sulfate minerals
Gypsum, anhydrate
Native elements
Gold, platinum, iron

27. Classification of Rock-Forming Minerals
CHECK YOUR NEIGHBOR
The silicates are the most common and abundant mineral group, because silicon and oxygen are
the hardest elements on Earth’s surface.
the two most abundant elements in the Earth’s crust.
found in the mineral quartz.
formed in a tetrahedral structure.
B) the two most abundant elements in the Earth’s crust.

28. Classification of Rock-Forming Minerals
CHECK YOUR ANSWER
The silicates are the most common and abundant mineral group, because silicon and oxygen are
the hardest elements on Earth’s surface.
the two most abundant elements in the Earth’s crust.
found in the mineral quartz.
formed in a tetrahedral structure.
B) the two most abundant elements in the Earth’s crust.

29. The Formation of Minerals and Rock
Minerals form by the process of crystallization.
Minerals crystallize from two primary sources:
Magma (molten rock)
Water solutions

30. The Formation of Minerals and Rock
Minerals crystallize systematically based on their respective melting points.
The first minerals to crystallize from a magma are those with the highest melting point and the lowest amount of silica.
The last minerals to crystallize from a magma are those with lower melting points and higher amounts of silica.

31. The Formation of Minerals and Rock
Water solutions associated with later stages of crystallization from magma account for many important ore deposits.
As water solutions become chemically saturated, minerals precipitate.
Ore deposits can be deposited into cracks or into the matrix of the rock itself.

32. The Formation of Minerals and Rock
Water solutions can precipitate chemical sediments such as carbonates and evaporites.
For chemical sediments, solubility rather than melting point determines which minerals will form first.
Low-solubility minerals precipitate first.
High-solubility minerals precipitate last.

33. The Formation of Minerals and Rock
CHECK YOUR NEIGHBOR
In the crystallization of chemical sediments from a water solution, low-solubility minerals precipitate first, because
they dissolve more easily.
they are more susceptible to being dissolved.
they are not easily dissolved.
they are infinitely soluble.
C) they are not easily dissolved.

34. The Formation of Minerals and Rock
CHECK YOUR ANSWER
In the crystallization of chemical sediments from a water solution, low-solubility minerals precipitate first, because
they dissolve more easily.
they are more susceptible to being dissolved.
they are not easily dissolved.
they are infinitely soluble.
C) they are not easily dissolved.

35. Rock Types
A rock is an aggregate of minerals—a physical mixture. The three categories of rock reflect how they were formed:
Igneous
Formed from cooling and crystallization of magma or lava
Sedimentary
Formed from preexisting rocks subjected to weathering and erosion
Metamorphic
Formed from preexisting rock transformed by heat, pressure, or chemical fluids

36. Igneous Rocks
Igneous rocks are formed from the cooling and crystallization of magma or lava.
Magma is molten rock that forms inside Earth.
Lava is molten rock (magma) erupted at Earth’s surface.

37. Igneous Rocks: Generation of Magma
Role of heat:
Temperature increases within Earth’s upper crust—the geothermal gradient—at an average rate of 30°C per kilometer.
Rocks in the lower crust and upper mantle are near their melting points.
Any additional heat (from rocks descending into the mantle or rising heat from the mantle) may help to induce melting.
Heat is a minor player.

38. Igneous Rocks: Generation of Magma
Role of pressure:
Reduced pressure lowers the melting temperature of rock.
When confining pressures drop, decompression melting occurs.
Analogies and examples:
The solid inner core
A pressure cooker

39. Igneous Rocks: Generation of Magma
Role of fluids
Fluids (primarily water) cause rocks to melt at lower temperatures.
Analogy: salt added to water causes ice to melt at a lower temperature.

40. Igneous Rocks CHECK YOUR NEIGHBOR
Even though the temperature at depth is hotter than rock’s melting point, the rocks at depth are solid, because
they are under enormous pressure from rock above.
increased pressure prevents their melting.
temperature would have to be even higher to counteract the increase in pressure.
all of the above.
D) all of the above.

41. Igneous Rocks CHECK YOUR ANSWER
Even though the temperature at depth is hotter than rock’s melting point, the rocks at depth are solid, because
they are under enormous pressure from rock above.
increased pressure prevents their melting.
temperature would have to be even higher to counteract the increase in pressure.
all of the above.
D) all of the above.

42. Igneous Rocks
The mineral makeup of igneous rock is dependent on the chemical composition of the magma from which it crystallizes.
Three types of magma:
Basaltic
Andesitic
Granitic

43. Igneous Rocks
Melting of rock into magma occurs over a broad temperature range.
Partial melting rules.
Minerals with low melting points (high silica content) are the first to melt.
Partial melting results in a silica-enriched magma.

44. Igneous Rocks
Minerals crystallize systematically based on their respective melting points.
Minerals with high melting points(low silica content) are the first to crystallize.
The process of crystallization acts to enrich the remaining magma with silica.
Minerals with low melting points (high silica content) are left in the melt.

45. Igneous Rocks
Igneous rocks are classified according to where they are formed.
Rocks formed from magma that crystallizes at depth are termed intrusive, or plutonic rocks.
Rocks formed from lava at the surface are classified as extrusive, or volcanic rocks.

46. Igneous Rocks There are three types of volcanoes: Shield Cinder cone
Composite

47. Igneous Rocks
Igneous rock that cools below Earth’s surface is called plutonic.
Granite is the most common plutonic rock.
Batholiths are large expanses of plutonic rock.

48. Sedimentary Rocks Sedimentary rocks are products of 4 processes:
Weathering
Erosion
Deposition
Sedimentation

49. Sedimentary Rocks
Weathering—the physical breakdown and chemical alteration of rock at Earth’s surface.
Two types of weathering:
Mechanical weathering—breaking and disintegration of rocks into smaller pieces.
Chemical weathering—chemical decomposition and transformation of rock into one or more new compounds.

50. Sedimentary Rocks: Mechanical Weathering
Frost wedging—alternate freezing and thawing of water in fractures and cracks promotes the disintegration of rocks.
Thermal expansion—alternate expansion and contraction due to heating and cooling.
Biological activity—disintegration resulting from plants and animals.

51. Sedimentary Rocks: Chemical Weathering
Main producer of sediment.
Breaks down rock components and the internal structures of
minerals.
Most important
agent is water.

52. Sedimentary Rocks: Erosion
Erosion—the physical removal of material by mobile agents such as water, wind, ice, or gravity.
Erosion does not occur in place. It involves movement.

53. Sedimentary Rocks: Deposition
Deposition — the stage in which eroded particles come to rest. Larger particles are the first to be deposited. Smaller particles are able to remain with the flow. In this way, sediments are sorted according to size as they are deposited.

54. Sedimentary Rocks: Sedimentation
During sedimentation, sediment particles are deposited horizontally layer by layer.
As deposited sediment accumulates, it changes into sedimentary rock.
Lithification occurs in two steps:
Compaction
Cementation

55. Sedimentary Rocks: Sedimentation
Compaction—Weight of overlying material presses down upon deeper layers.
Cementation—Compaction releases “pore water” rich in dissolved minerals. This mineralized “pore water” acts as a glue to cement sediment particles together.

56. Sedimentary Rocks: Classifying Sedimentary Rocks
Sedimentary rock types are based on the source of the material:
Clastic rocks—transported sediment particles—bits and pieces of weathered rock (shale, sandstone, conglomerate)
Chemical rocks—sediments that were once in solution (travertine, halite, limestone)

57. Clastic Sedimentary Rocks classified by particle size
Shale
Mud-sized particles in thin layers
Most common sedimentary rock
Sandstone
Composed of sand-sized particles
Quartz is the predominant mineral
Conglomerates
Composed of particles greater than 2 mm in diameter
Consists largely of rounded gravels

58. Chemical Sedimentary Rocks
Limestone:
Most abundant chemical rock.
Composed chiefly of the mineral calcite.
Marine biochemical limestones form as coral reefs, coquina (broken shells), and chalk (microscopic organisms).

59. Chemical Sedimentary Rocks
Evaporites:
Evaporation triggers the deposition of chemical precipitates.
Examples include rock salt and rock gypsum.

60. Chemical Sedimentary Rocks
Coal:
Different from other rocks, because it is composed of organic material.
Stages in coal formation (in order):
Plant material
Peat
Lignite
Bituminous coal
Anthracite coal

61. The most characteristic feature of sedimentary rocks is
CHECK YOUR NEIGHBOR
The most characteristic feature of sedimentary rocks is
they contain fossils.
the lithification and cementation of sediments.
the layered sequence of strata.
the fusing of unconsolidated sediments into solid rock.
C) the layered sequence of strata.

62. The most characteristic feature of sedimentary rocks is
CHECK YOUR ANSWER
The most characteristic feature of sedimentary rocks is
they contain fossils.
the lithification and cementation of sediments.
the layered sequence of strata.
the fusing of unconsolidated sediments into solid rock.
C) the layered sequence of strata.

63. Metamorphic Rocks Metamorphic rocks are produced from:
Igneous rocks
Sedimentary rocks
Other metamorphic rocks
Metamorphism occurs via recrystallization and mechanical deformation.

64. Metamorphic Rocks Contact metamorphism:
a body of rock is intruded by magma
is typically associated with high temperatures and high water content—lots of chemical activity, not much, or no, mechanical deformation.

65. Metamorphic Rocks Regional metamorphism:
the alteration of rock by both heat and pressure over an entire region rather than just near a contact between rock bodies.

66. Metamorphic Rocks
Metamorphic rock is defined by appearance and mineral content:
Foliated—layered in sheets (schist, slate, gneiss)
Nonfoliated—not layered (marble and quartzite)

67. Marble is an example of:
Metamorphic Rocks
CHECK YOUR NEIGHBOR
Marble is an example of:
Crystalline, metamorphosed limestone.
Foliated metamorphic rock.
Recrystallized sandstone.
Nonfoliated mica.
A) Crystalline, metamorphosed limestone.

68. Marble is an example of:
Metamorphic Rocks
CHECK YOUR ANSWER
Marble is an example of:
Crystalline, metamorphosed limestone.
Foliated metamorphic rock.
Recrystallized sandstone.
Nonfoliated mica.
A) Crystalline, metamorphosed limestone.

69. The Rock Cycle
Molten rock rises from the depths of Earth, cools, solidifies, and eventually returns to become magma again.