R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
CHAPTER 2
MINERALS AND ROCKS
OUTLINE
INTRODUCTION
MATTER AND ITS COMPOSITION
Elements and Atoms
Bonding and Compounds
MINERALS—THE BUILDING BLOCKS OF ROCKS
How Many Minerals Are There?
Rock-Forming Minerals and the Rock Cycle
IGNEOUS ROCKS
Texture and Composition
Classifying Igneous Rocks
SEDIMENTARY ROCKS
Sediment Transport, Deposition, and Lithification
Classification of Sedimentary Rocks
METAMORPHIC ROCKS
What Causes Metamorphism?
Metamorphic Rock Classification
PLATE TECTONICS AND THE ROCK CYCLE
SUMMARY
CHAPTER OBJECTIVES
The following content objectives are presented in Chapter 2:
 Chemical elements are composed of atoms, all of the same kind, whereas compounds
form when different atoms bond together. Most minerals are compounds, which are
characterized as naturally occurring, inorganic, crystalline solids.
 Of the 3,500 or so minerals known, only a few, perhaps two dozen, are common in
rocks, but many others are found in small quantities in rocks and some are important
natural resources.
 Cooling and crystallization of magma or lava and the consolidation of pyroclastic
materials account for the origin of igneous rocks.
 Geologists use mineral content (composition) and textures to classify plutonic rocks
(intrusive igneous rocks) and volcanic rocks (extrusive igneous rocks).
 Physical and chemical weathering yields sediment that is transported, deposited, and
then lithified to form detrital and chemical sedimentary rocks.
 Texture and composition are the criteria geologists use to classify sedimentary rocks.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
 Any type or rock may be altered by heat, pressure, fluids, or any combination of
these, to form metamorphic rocks.
 One feature used to classify metamorphic rocks is foliation—that is, a platy or layered
aspect,but some lack this feature and are said to be nonfoliated.
 The fact that Earth materials are continually recycled and that the three families of
rocks are interrelated is summarized in the rock cycle.
LEARNING OBJECTIVES
To exhibit mastery of this chapter, students should be able to demonstrate comprehension
of the following:
 the nature of minerals, including the classification of substances as mineral or not
mineral
 the basic atomic structure, and the formation of elements and compounds
 the types of minerals and their roles in the various types of rocks
 the rock cycle, including how each type of rock can yield the other rock types
 the formation and classification of igneous rocks
 sediment production through weathering, environments of deposition, and
lithification
 the formation and classification of metamorphic rocks
 the effects of plate tectonics on the rock cycle
CHAPTER SUMMARY
1. Minerals are naturally occurring, inorganic, crystalline solids with distinctive
physical properties and specified chemical compositions. Rocks are made of one or
more minerals.
Figure 2.1
Minerals and Rock
2. Elements are composed of atoms, which have a nucleus of protons and neutrons
around which electrons occupy electron shells.
Figure 2.2
Shell Model for Atoms
3. The number of protons in a nucleus determines the atomic number of an element;
the atomic mass number is the number of protons plus neutrons in the nucleus. The
number of neutrons in the nucleus of an element may vary, forming different
isotopes of the element.
Figure 2.3
Isotopes of Carbon
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
4. Atoms join together or bond by transferring electrons from one atom to another
(ionic bond) or by sharing electrons (covalent bond). Most minerals are compounds
of two or more different elements bonded together.
Figure 2.4
Ionic and Covalent Bonding
5. Atoms of minerals are arranged in a specific three dimensional framework.
Although some minerals have a specific chemical composition, other minerals have
a compositional range because of substitution.
Figure 2.5
A Variety of Mineral Crystal Shapes
6. By far the most common minerals are the silicates (composed of silicon and
oxygen), but carbonate minerals (containing the CO32- ion) are prevalent in some
rocks.
Figure 2.6
Some of the Common Silicate Minerals
Table 2.1
Some of the Mineral Groups Recognized by Geologists
Enrichment Topic 1. Gemstones
Some minerals qualify as collectible and valuable. Your students can investigate the
various types of gemstones that are considered precious through this PBS website
(http://www.pbs.org/wgbh/nova/diamond/gemprimer.html ). The formulas of gemstones
can be accessed at http://pubs.usgs.gov/gip/gemstones/formulas.html , and from these
you may want to consider having your students classify gemstones into their
corresponding mineral groups. Physical properties of minerals are listed at
http://www.gemstone.org/gem-by-gem/gem-by-gem.html , while this USGS website
discusses environments of formation:
http://pubs.usgs.gov/gip/gemstones/environment.html.
7. The rock cycle demonstrates that the three families of rocks—igneous,
sedimentary, and metamorphic—are interrelated.
Figure 2.7
The Rock Cycle
8. The two broad groups of igneous rocks, intrusive (or plutonic) and extrusive (or
volcanic) are classified by composition and texture. However, for a few extrusive
rocks, texture is the main consideration.
Figure 2.8
Block Diagram Showing Plutons or Intrusive Bodies of Igneous
Rock
Figure 2.9
Igneous Rock Textures
Figure 2.10 Classification of Igneous Rocks
Figure 2.11 The Common Igneous Rocks
Figure 2.12 The Igneous Rocks in this Chart are Classified Mainly by their
Textures
9.
Lithification involving compaction and cementation is the process whereby
sediment is transformed into sedimentary rock.
Figure 2.13 Lithification and Classification of Detrital Sedimentary Rocks
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
10. Sedimentary rocks are also grouped into two broad categories: detrital (made up of
solid particles of preexisting rocks) and chemical/biochemical (composed of
minerals derived by inorganic chemical processes or the activities of organisms).
Figure 2.14 Detrital Sedimentary Rocks
Figure 2.15 Chemical Sedimentary Rocks
Table 2.2
Classification of Chemical and Biochemical Sedimentary Rocks
Figure 2.16 Evaporites, Chert, and Coal
11. Metamorphic rocks result from compositional and/or textural transformation of
preexisting rocks by heat, pressure, and fluid activity. Most metamorphism is
regional, occurring deep within the crust over large areas. However, some
metamorphism (contact metamorphism) occurs when rocks adjacent to an igneous
body are altered.
12. Metamorphic rocks result from compositional and/or textural transformation of
other rocks by heat, pressure, fluid activity, or a combination of these agents. Most
metamorphism is regional, occurring deep within the crust over large areas, but
some, called contact metamorphism, takes place adjacent to hot igneous rocks.
Dynamic metamorphism occurs in zones adjacent to faults where high levels of
differential pressure develop.
13. Metamorphism imparts a foliated texture to many rocks (parallel alignment of
minerals), but some rocks have a mosaic of equidimensional minerals and are
nonfoliated.
Figure 2.17 Foliated Texture
14. The several varieties of metamorphic rocks are classified largely by their textures,
but composition is a consideration for some of these rocks.
Table 2.3
Classification of Common Metamorphic Rocks
Figure 2.18 Foliated Metamorphic Rocks
Figure 2.19 Nonfoliated Metamorphic Rocks
15. Plate tectonics, which is driven by Earth’s internal heat coupled with surface
processes such as weathering, erosion, and deposition, accounts for the recycling of
Earth materials in the rock cycle.
Enrichment Topic 2. “Your House Comes Out of a Mine.”
Rocks and minerals provide many of the natural resources for the physical structures we
build. “If you don’t grow it, you mine it.” Have students investigate the grand variety of
raw materials supplied by the mined rocks and minerals in the building industry. The
USGS mineral website (http://www.usgs.gov/themes/mineral.html) discusses various
commodities. Some mined natural resources are discussed within a collection of fact
sheets (http://water.usgs.gov/wid/index-resources.html).
The Mineral Information Institute (http://www.mii.org/commonminerals.php) also lists
the common minerals and their uses.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
Students can investigate the materials within their own dwellings, and identify them as
far as the mineral or rock type, and the location from which items are mined. Some
possibilities include aluminum, gypsum (for sheetrock/wallboard), clay, and sand.
The more obvious “rock” building materials—such as that used as flooring material,
countertops, or fireplace hearths—are usually classified by building contractors as
“marble” or “granite.” However, there are a variety of rocks that are used in construction
which are not marble or granite! Students can investigate these various rock countertops
and floor tiles, and correctly classify them using the information in the chapter.
LECTURE SUGGESTIONS
The Nature of Minerals and Rocks
Students can explore the characteristics that substances must possess in order to classify
as minerals. In particular, the instructor may explore organic composition, liquid phases,
and man-created gemstones.
1. Is the element mercury a mineral by our definition? Why or why not? Does glacial
ice classify as a mineral?
2. If a laboratory gemstone has identical composition and physical properties as a
substance found in nature, is it a mineral? Does coal classify as a mineral? Ask
students to think of examples where a substance may classify as a rock, but it is not
made of minerals.
Common Rock-Forming Minerals
Students can learn more about the common rock-forming minerals. Although there are
over 3,500 different minerals, only a few are common within rocks. About.com Geology
lists the common minerals that are abundant and widespread, the accessory minerals that
are widespread but rarely abundant, and interesting but uncommon minerals.
(http://www.mii.org/commonminerals.php) Each mineral has a clickable link that
includes a photograph of the mineral, as well as a general description. Ask your students
to locate the formulas of the common rock-forming minerals, and then classify them into
the mineral groups recognized by geologists (Table 2.1).
Rock Types
If students are presented with an assortment of rocks, how would they begin determining
which were sedimentary, which were metamorphic, and which were igneous? Discuss the
characteristics of the rocks types, including clastic texture, foliation, and crystalline
composition.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
The Nature of Sedimentary Rocks
Detrital sedimentary rocks are classified primarily by the size of the included particle, not
composition. Students should discuss the common meaning of the words “sand” and
“clay.” “Sand” and “clay” are used as categories of particle size, although we commonly
use “sand” to convey “quartz composition.” (If the green beach sands of Hawaii, which
are composed partly of the mineral olivine, were lithified, olivine sandstone would result.
Conversely, a sedimentary rock composed of sand-sized feldspar grains is commonly
referred to as an “arkose.”). “Clay” is another term that can be used as both a size
category, as well as a group of minerals.
The Rock Cycle
Discuss the various paths that rocks can take within the rock cycle, and how one rock
type can be transformed into all the other rock types.
1. Can a sedimentary rock form metamorphic rock and igneous rock? Discuss a
pathway by which an existing sedimentary rock can become a new sedimentary
rock.
2. How does the processing of Earth materials through the various transitions of the
rock cycle affect the aspects of the rocks that allow us to date them? In which
types of rocks do we find fossils? Are these fossils preserved if the rock
containing the fossils is transformed to other rock types within the rock cycle?
CONSIDER THIS
1. How can you identify a nonfoliated metamorphic rock, such as marble, from the
original rock? What characteristics might nonfoliated metamorphic rocks have that
make their identification easier? Would nonfoliated metamorphic rocks be easier to
identify in the field, rather than in the laboratory as an assortment of samples?
2. Can we identify specific environments associated with plate tectonic boundaries in
which various rock types would form? Are igneous rocks associated with
convergent, divergent, and transform plate boundaries? In which environments are
metamorphic, and sedimentary, rocks produced?
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
IMPORTANT TERMS
atom
atomic mass number
atomic number
bonding
carbonate mineral
carbonate rock
chemical sedimentary rock
compound
contact metamorphism
crystalline solid
detrital sedimentary rock
dynamic metamorphism
Element
evaporite
extrusive igneous volcanic rock
geologic record
igneous rock
intrusive igneous plutonic rock
Lava
lithification
magma
metamorphic rock
mineral
pyroclastic material
regional metamorphism
rock
rock cycle
rock-forming mineral
sedimentary rock
silicate
SUGGESTED MEDIA
Videos
1. Minerals: The Materials of Earth, Earth Revealed #12, Annenberg/CPB
2. Intrusive Igneous Rocks, Earth Revealed #14, Annenberg/CPB
3. Metamorphic Rocks, Earth Revealed #18, Annenberg/CPB
4. Rocks and Minerals, Cambridge Educational Products
5. Standard Deviants School Geology Minerals, Cerebellum Corporation
6. Standard Deviants School Geology, Sedimentary & Metamorphic Rocks,
Cerebellum Collection
7. Core Geology, Ambrose Video
8. Igneous Rocks, Ambrose Video
9. Introduction to Rocks and Minerals, Ambrose Video
10. Metamorphic Rocks, Ambrose Video
11. Sedimentary Rocks, Ambrose Video
Software
1. Hands-On Mineral Identification, Tasa Graphics Arts, Inc.
2. The Study of Minerals, Tasa Graphics Arts, Inc.
3. Tasa Photo CD-ROM, Rock Cycle I, Tasa Graphics Arts, Inc.
4. The Wonders of Rocks and Minerals, Tasa Graphics Arts, Inc.
5. Study of Minerals, RockWare, Inc.
6. Explore Silicate Minerals, Geological Society of America
Slides and Demonstration Aids
1. Rocks and Topography, slide set, Educational Images, Ltd.
2. Rock Specimens and Crystals, slide set, Educational Images, Ltd.
3. Introductory Earth Science Rocks and Minerals, Science Stuff
4. Natural Crystal Collection, Science Stuff
5. Ores of Common Metals, rock collection, Science Stuff
6. Advanced Rock & Minerals Collection, Science Stuff
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
CHAPTER 2 - ANSWERS TO QUESTONS IN TEXT
Multiple Choice Review Questions
1.
2.
3.
4.
b
c
e
a
5.
6.
7.
8.
b
c
d
a
9. a
10. d
Short Answer Essay Review Questions
11. Plutonic rocks cool from magma below the Earth’s surface. These rocks cool
slowly and have larger, better-formed crystals. Volcanic rocks that from in a lava
flow at the Earth’s surface are extrusive. These rocks cool more rapidly and have
smaller or nonexistent crystals. Plutonic rocks include granite and gabbro. Some
volcanic rocks are rhyolite, basalt, and obsidian.
12. Atoms are the building blocks of elements, or the smallest particles that retain the
properties of an element. Elements are composed of only one kind of matter, and
have only one kind of atom. When two or more atoms combine chemically, they
form molecules. Molecules are the smallest units of compounds that still retain the
properties of the compound.
13. When ions of two elements have similar sizes, and the same electrical charge, they
can substitute for each other in the crystal framework. (Both ions “fit” within a
given space, and maintain the overall electrical neutrality of the compound.)With
olivine, the iron and magnesium ions are about the same size, and have the same
electrical charge.
14. As sand or mud accumulates, compaction occurs from the overlying sediments.
This reduces the pore space and the volume of the deposits. Compaction is using
sufficient for the lithification of mud. For sand participles, cementation is also
necessary, and this involves the precipitation of minerals within the pores. This
binds the sand sediments. Sand-size sediments produce sandstone upon
lithification, while mud-size sediments produce mudrocks. If the mudrock is
composed of only silt-sized particles, siltsone results. If the mudrock is composed
of only clay-sized particles, a claystone results. A shale is a claystone which is
fissile.
15. Contact metamorphism occurs when heat and chemical fluids from an igneous body
alter adjacent rocks. The degree of metamorphism decreases with increasing
distance from the body of magma until the surrounding rocks are unaffected. A
type of rock that forms from contact metamorphism is hornfels. Regional
metamorphism takes place over large but elongated areas as the result of
tremendous pressure, elevated temperatures, and fluid activity. This type of
metamorphism is most obvious along convergent plate boundaries where the rocks
are intensely deformed during convergence and subduction. It can also occur along
divergent boundaries. Gneiss is found in areas with regional metamorphism.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
16. The definition of mineral states that the substance must be in the solid phase. Ice is
the solid phase of H2O, while liquid water and water vapor are not.
17. Evaporites form by inorganic chemical precipitation of minerals from solutions that
are concentrated by evaporation. Common evaporites include rock salt and rock
gypsum.
18. Conglomerates and sedimentary breccias are detrital sedimentary rocks. Both are
made of gravel-sized particles (particles greater than 2 mm), but a conglomerate has
rounded clasts, while a sedimentary breccia has angular clasts.
19. The physical properties of pyrite, galena, and halite differ so that it is possible to
distinguish them apart. Pyrite is generally brassy yellow in color with a metallic
luster. Although galena also possesses a metallic luster, it is generally lead grey in
color, and has a much lower hardness than pyrite. Pyrite can scratch galena, but
galena cannot scratch pyrite. Halite is distinguishable from galena and pyrite
because it has a nonmetallic luster, and it generally colorless or white. Halite can
also be easily distinguished by its salty taste.
20. Silicate minerals include a combination of silicon and oxygen. The subgroups are
ferromagnesian silicates, which contain iron, magnesium or both, and
nonferromagnesian silicates, which lack these elements. Ferromagnesian minerals
are darker and denser than nonferrmagnesian ones.
Apply Your Knowledge
1. Specimen 1 is a volcanic, extrusive igneous rock because visible crystals are not
obvious. Conversely, Specimen 2 has larger crystals, a phaneritic texture, and will
classify as a plutonic, intrusive igneous rock. Based on the compositions given,
Specimen 1 is basalt, and Specimen 2 is granite.
2. You could use a salad analogy to distinguish between minerals and rocks. A salad is
composed of many different ingredients, such as lettuce, carrot slices, and tomatoes.
All of these ingredients produce a unique salad. A small variation in the amount of
carrots, lettuce, or tomatoes will still produce a typical “garden salad,” but if we
vary the composition to include boiled shrimp and crabmeat, we would have to
reclassify our salad as a “seafood salad.” With this analogy, the individual salad
vegetables and ingredients are the “minerals” and the resulting composite salad is
the “rock.” Changing the minerals will change the rock type.
3. The clasts in Figure 2.14a were transported the greater distance when compared
with the clasts in Figure 2.14b. The clasts in 2.14a are more rounded, and rounding
results from wear and abrasion of transport. Conversely, the angular particles of the
breccia were not transported a great distance before deposition. The clasts would be
more rounded if they were transported any distance from the source.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
4. Sedimentary Rocks: Sedimentary, metamorphic, and igneous rocks at the Earth’s
surface can be weathered and eroded into sediment. These sediments are
thentransported and deposited. Over time, compaction (rom the overburden) and
cementation result in lithification. Sedimentary rocks result.
Metamorphic Rocks: Sedimentary, metamorphic, and igneous rocks may be
metamorphosed through contact with magma or lava (contact metamorphism),
along a fault zone (dynamic metamorphism), or within large areas where mountain
building is taking place. As long as heat, pressure, and/or fluid activity results in the
solid state transformation of an existing rock, new metamorphic rocks result.
Igneous Rocks: Sedimentary, metamorphic, and igneous rocks may be heated to
the melting point, form magma, and then cool to form new igneous rocks. The
magma may cool below the Earth’s surface to form plutonic intrusive igneous
rocks, or erupted to the Earth’s surface and cool from lava to form volcanic
extrusive igneous rocks.
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