1. Chapter 17
Rocks and Minerals

2. Composition of the Earth
During the early molten stage of the Earth the heavier abundant elements, such as iron and nickel, sank to the deep interior of the earth, leaving the lighter elements on the surface.
This thin layer on top of the earth is called the crust.
Only 8 elements make up about 98.6% of the crust. All other elements make up the remaining 1.4%.
Oxygen is the most abundant element, about 50% of the crust as part of compounds. Silicon makes up over 25%.
The solid materials of the earth’s crust are known as minerals and rocks.

3. Fig. 17.2

4. Composition of the Earth
About 2,500 minerals exist but only about 20 are common in the crust, for example quartz, calcite, and gypsum
Minerals are the fundamental building blocks of the rocks that make the earth’s crust.
A rock is a solid aggregation of one or more minerals that have been cohesively brought together by a rock-forming process.
Examples of common rocks are sandstone, limestone, and granite.

5. Minerals
A mineral is defined as a naturally occurring, inorganic solid element or compound with a crystalline structure.
The element or compound:
1. cannot be synthetic (must be naturally
occurring)
2. must not be produced by a living
organism (must be inorganic)
3. must have atoms arranged in a regular,
repeating pattern (a crystal structure).
The crystal structure of a mineral can be present on the microscopic scale and it is not necessarily obvious to the unaided eye.

6. A crystal is composed of a structural unit that is repeated in 3 dimensions.
This is the basic structural unit of a crystal of sodium chloride, the mineral halite.

7. The structural unit for a crystal of table salt, sodium chloride, is cubic,
as you can see in the individual grains.

10. Crystal Structures
The crystal structure of a mineral can be made up of atoms of one or more kinds of elements.
Diamond is a mineral with only carbon atoms in a strong crystal structure.
Quartz is a mineral with atoms of silicon and oxygen in a different crystal structure. Minerals have well defined chemical compositions or a range of chemical compositions.

11. Crystals
Crystals can be classified and identified on the basis of the symmetry of their surfaces.
The symmetry is an outward expression of the internal symmetry in the arrangement of the atoms making up the crystal.
On the basis of symmetry crystalline substances are classified into 6 major systems which in turn are subdivided into smaller groups.

12. Basic crystalline systems

13. Quartz crystals
are hexagonal
Fig. 17.5

14. Silicates and Nonsilicates
The most abundant minerals contain silicon and oxygen, since they are the most abundant elements on Earth.
All minerals are classified on the basis of whether they contain these two elements or not. The two main groups are thus the silicates and nonsilicates. The silicates can contain other elements in addition to silicon and oxygen.
The silicate minerals are by far the most abundant, making up about 92% of the earth’s crust.

15. Silicates
Si and 4 Oxygen atoms from a tetrahedral ionic structure, SiO42-.
All silicates contain SiO42- and it can combine with metallic ions, for example ions of iron or magnesium. (ferromagnesian silicates)
The SiO42- can also combine with the silicon atoms of other tetrahedral units.
(nonferromagnesian silicates)

16. a tetrahedron, which has four equal sides.
The geometric shape of
a tetrahedron, which has
four equal sides.
A silicon with four oxygen
Atoms are arranged in the
shape of a tetrahedron with
The silicon in the center.
This is the basic building block
of all silicate minerals.

17. Silicate Minerals Silicate minerals can be divided into:
1. ferromagnesian silicates-The basic tetrahedral structure joins with ions of iron, magnesium, calcium, and other metals. They have a darker color and greater density than the other silicates because of the presence of the metal ions.
2. nonferromagnesian silicates-Do not contain iron or magnesium ions. These minerals have a light color and a low density compared to the ferromagnesians. Quartz, a very well known mineral belongs here.

18. Dark colored ferromagnesian silicates: Augite is on the right and hornblende
is on the left.

19. Ferromagnesian Silicates
Olivine
Biotite
Hornblende
Augite

20. Light colored nonferromagnesian silicates mica (front center), white and pink orthoclase
(top center), and quartz (left).

21. Nonferromagnesian Silicates
Orthoclase
Quartz
Mica (muscovite)

22. Nonsilicate Minerals There are 8 subgroups:
carbonates 2. sulfates oxides
4. sulfides 5. halides 6. phosphates
7. hydroxides 8. native elements
The carbonates are the most abundant of the nonsilicates but others are important as fertilizers, sources of metals and sources of industrial chemicals.

23. Non-silicates
hematite
dolomite
apatite
halite
gypsum
galena
gold

25. Minerals to Know:
Ferromagnesian Silicates: augite, hornblende, olivine
Nonferromagnesian Silicates: quartz, mica, orthoclase, talc
Nonsilicates: All native elements, also gypsum (CaSO4), galena, halite (NaCl), apatite, dolomite (MgCO3), hematite, calcite (CaCO3)

26. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density

27. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
Often misleading, quartz for example comes in many colors but its true color is clear.

28. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
Although the color may be misleading, when rubbed across a tile, the streak often reveals the ‘true’ color of the mineral.

29. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density

30. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
Talc, hardness of 1

31. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
Quartz, hardness of 7

32. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
The most useful clue.

33. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
How the mineral breaks along smooth
planes. This is when they have zones
of weakness.

34. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
How the mineral fractures. This occurs
when they do not have areas of weakness.
The broken surface is irregular and not in
the flat plane of a cleavage.

35. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
The sheen. Examples are metallic, pearly, vitreous (glassy) and earthy.

36. Physical properties of minerals
8 characteristics to determine the mineral.
Color
Streak
Hardness
Crystal form
Cleavage
Fracture
Luster
density
Mass divided by volume

37. Mineral Forming Processes
Mineral crystals usually form in a liquid environment, but they can also form from gases or in solids under the right conditions.
Two liquid environments where minerals can form are water solutions and solutions of a hot, molten mass of melted rock materials.
The molten rock material from which minerals crystallize is known as magma. It can cool and crystallize to solid minerals either below or on the surface of the earth.
Magma which is forced out to the surface of the earth is also called lava, the molten material associated with volcanoes.

38. Mineral Forming Processes
When minerals form from solutions the dissolved ions must be very concentrated. Their charges can pull them together and crystals can form.
Mineral forming processes are influenced by:
Temperature
Pressure
Time
Availability and concentrations of ions in solution

39. Mineral Forming Processes
Large crystals result from slow cooling of magma or from high water content in the magma (very dilute solutions).
Small or even microscopic crystals result from rapid cooling and low water content (very concentrated solutions).
Sudden chilling can prevent crystal growth altogether, resulting in glass, a solid that cooled too quickly for its atoms to move into ordered crystal structures (amorphous solid).

40. Ore Minerals
If mineral deposits have an economic value they are called ore minerals. They are left over from crystallizing magna and crystallize in rock fractures to form thin, flat bodies of mineral material called veins.
Some native elements can occur as ore minerals. They include copper, diamond, gold, silver, and sulfur.

41. Rocks
A rock is defined as an aggregation of one or more minerals and perhaps other materials that have been brought together into a cohesive solid.
They include volcanic glass, a silicate that is not considered a mineral because it lacks a crystalline structure.
A rock can consist of one or more kinds of minerals that are somewhat “glued” together by other materials such as glass.
Granite is a rock that is primarily three silicate minerals: quartz, mica, and feldspar. You can see the grains of the 3 minerals in the freshly broken surface of most granites.

42. Granite is a coarse-grained igneous rock composed mostly of light-colored, light-density
Nonferromagnesian minerals. The earth’s continental areas are dominated by granite and
by rocks with the same mineral composition as granite.

43. Rocks
There are 3 main groups of rocks that are based on the way that rocks form:
1. Igneous rocks are formed as a hot, molten mass of rock materials cooled and solidified.
2. Sedimentary rocks are formed from particles of dissolved materials from previously existing rocks.
3. Metamorphic rocks are from rocks that were subjected to high temperatures and pressures that deformed or recrystallized the rock without complete melting.

44. Igneous Rocks
Ignis means “fire”. Temperatures hot enough to melt the rocks are required.
Magma may cool and crystallize to solid igneous rock either below or on the surface of the earth.
All rocks at one time were igneous rocks. Today about two thirds of the outer layer, or crust, is made up of igneous rocks.
The texture of the igneous rocks depends on how rapidly the cooling of the magma takes place. The more rapidly the magma cools the more coarse the texture is. Very rapidly cooling magma results in volcanic glass.

45. Igneous Rocks Formed as hot, molten mass of rock materials.
Rhyolite and obsidian are the chemical equivalents of granite, except they are
different in texture. Rhyolite is fine grained and obsidian is a translucent volcanic glass.
Granite
Obsidian
Rhyolite

46. Igneous Rocks Formed as hot, molten mass of rock materials.
Granite less dense than basalt, makes up most of continental crust.
Basalt makes up most of oceanic crust.
Granite
Basalt

47. Sedimentary Rocks
Sedimentary rocks are rocks that formed from particles or dissolved materials from previously existing rocks. They are transported by moving water and are deposited as sediments.
Sediments are accumulations of silt, sand, or other materials that settle out of water.

48. Sedimentary Rocks There are two types of sedimentary rocks:
1. Clastic sediments-Weathered rock fragments.
2. Chemical sediments-Dissolved rock material.

49. Gypsum is calcium sulfate (CaSO4)

50. Because the gypsum from the quarries of the Montmartre district of Paris has long furnished burnt gypsum used for various purposes, this material has been called plaster of Paris. It is used to make drywall.
Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O.
Gypsum is a very common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. The largest deposits known occur in strata from the Permian age. Gypsum is deposited in lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins.

51. This is a sample of breccia, a coarse grained sedimentary rock with coarse,
angular fragments.

52. This is a sample of sandstone, a sedimentary rock that formed from sand grains in
a matrix of very fine grained silt, clay, or other materials. The grains in this sample
are mostly feldspar and quartz minerals, which probably accumulated near the granite
from which they were eroded.

53. Chemical Sedimentary Rocks
Carbonates and evaporates are the most common sedimentary rocks.
The carbonates are limestone and dolomite.
Limestone is composed of calcium carbonate (CaCO3). This is also the composition of the mineral called calcite. It is precipitated directly from freshwater or salt water or indirectly by the actions of plants and animals that form shells of calcium carbonate.
Dolomite is magnesium carbonate (MgCO3).

54. This is a sample of limestone, a sedimentary rock made of calcium carbonate that
formed under water directly or indirectly from the actions of plants and animals.
This fine grained limestone formed indirectly from the remains of tiny marine organisms.

55. Lithification of sand grains to become sandstone.
Lithification means rock formation.
Loose sand grains are deposited with open pore space between the grains.
The weight of overburden compacts the sand into a tighter arrangement,
reducing the pore space.
C. Precipitation of cement in the pores by groundwater binds the sand into the
rock sandstone, which has a clastic texture.

56. Metamorphic Rocks
Metamorphic Rocks are previously existing rocks that have been changed by heat, pressure, or hot solutions into a distinctly different rock.
The heat, pressure, or hot solutions that produced the changes are associated with geologic events, such as movement of the crust and heating and hot solutions from intrusion of a magma.
Pressures from movement of the crust can change the rock texture by flattening, deforming, or realigning mineral grains.
Temperatures from an intruded magma must be just right to produce a metamorphic rock They must be high enough to disrupt the crystal structures to cause them to recrystallize, but not high enough to melt the rocks and form igneous rocks.

57. Increasing metamorphic change occurs with increasing temperature and pressures.
If the melting point is reached, the change is no longer metamorphic and igneous
rocks are formed.

58. This banded metamorphic rock is very old; at an age of 3
This banded metamorphic rock is very old; at an age of 3.8 billion years, it is probably
the oldest rock on the surface of the earth. It was formed in Greenland.

59. This is sample of marble, a coarse-grained metamorphic rock with interlocking calcite
crystals. The calcite crystals were recrystallized from limestone during metamorphism.

60. Rocks to remember: Igneous: granite, obsidian, rhyolite Sedimentary:
Clastic: breccia, sandstone (made from
sand), shale (made from silt and clay)
Chemical: limestone (made from calcite),
dolomite, gypsum,
salt (made from halite)
Metamorphic: Marble, slate, schist, gneiss

61. The Rock Cycle
Earth is a dynamic planet with constantly changing surface and interior.
Internal changes alter the earth’s surface by moving the continents and building mountains that are eventually worn away by weathering and erosion.
Seas advance and retreat over the continents as materials that are cycled from the atmosphere to the land and from the surface to the interior of the earth and then back again.
Rocks are transformed from one type to another through this continental change.
There is not a single rock on the earth’s surface today that has remained unchanged through the earth’s long history.
The concept of continually changing rocks through time is called the rock cycle.

62. The Rock Cycle -Rock forming Process.
A schematic diagram of the rock cycle concept, which states that geologic
processes act continuously to produce new rocks from old ones.

63. Exercises Applying the concepts. p 441: # 1, 2, 3, 4, 6, 7, 8, 9, 11.
New Book: p # 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 27, 28, 29, 32, 33, 34, 36, 39, 40, 41, 42, 43, 44, 45.

64. Summary Chapter 17
Most common elements on earth’s crust: 1. oxygen and 2. silicon.
Earth’s crust is made up of minerals and rocks. Rocks are made up of minerals.
What is a mineral.
What is a crystal-they have 6 different symmetries and the simplest is the cubic. e.g. NaCl.
Silicates and nonsilicates (presence of Si and O)
Ferromagnesian (dark color and high density) and nonferromagnesian silicates (light color and low density) differ by presence of Fe and Mg in addition to Si and O.
Carbonates are the most abundant of the nonsilicates but others are important as fertilizers, sources of metals and sources of industrial chemicals.
Know the specific minerals indicated on slide.
What each of the 8 physical properties of minerals represent. The most useful is the crystal structure.
What are magma and lava.
Minerals form from solutions of dissolved ions in water or from magma that has cooled and solidified. The crystal structure is affected by T, P, and ion concentration. The slower the crystallization process and the more dilute the larger the crystals formed.
Ore minerals include native elements: copper, diamond, gold, silver, and sulfur and occur in veins.
Glass is a solid that cooled too quickly for its atoms to move into ordered crystal structures.
3 types of rocks: igneous, sedimentary and metamorphic. Sedimentary can be clastic or chemical.
Granite and basalt are the most abundant igneous rocks. All rocks at one time were igneous rocks.
Know the specific rocks indicated on slide.
The rock cycle. It originates with the igneous rocks.