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3. ROCKS
AND MINERALS
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5. Rocks and Minerals

6. Contents PHOTOGRAPH ON PAGE 1
A stone with a blue opal in its
center is a product of time, since
it forms over millions of years.
Dynamics of
the Earth's Crust
Page 6
Minerals
Page 18
Formation and
Transformation
of Rocks
Page 40
Classes of Rocks
Page 60
Use of Rocks
and Minerals
Page 76

7. THE MONK'S HOUSE
This orthodox monk lives in a
volcanic cave, very close to the
11 Christian churches located in
the Ethiopian town of Lalibela.
thing is that there will be rocks. Only
stones will remain, and their chemical
composition, shape, and texture will
provide clues about previous geological
events and about what the Earth's surface
was like in the past. In the pages of this
book, illustrated with stunning images, you
will find invaluable information about the
language of rocks and natural forces in
Memory of silent witnesses to the cataclysms our
planet has experienced. They know the
cold of the glacial era, the intense heat of
general. You will also learn to identify the
most important minerals, know their
physical and chemical properties, and
the Planet the Earth's interior, and the fury of the
oceans. They store much information
about how external agents, such as wind,
discover the environments in which they
form.
rain, ice, and temperature changes, have id you know that the Earth's crust
R
ocks, like airplane flight recorders,
store in their interior very useful
information about what has
been altering the planet's surface for
millions of years. D and its oceans are sources of useful
and essential minerals for human
beings? Coal, petroleum, and natural gas
happened in the past. Whether forming or ancient civilizations, stones found in the crust allow us to travel and to
caves in the middle of mountains, mixed
among folds, or lying at the bottom of
lakes and oceans, stones are everywhere,
F symbolized eternity. This idea has
persisted throughout time because
stones endure, but they are recycled time
heat our homes. Furthermore, practically all
the products that surround us have
elements provided by rocks and minerals.
and they hold clues to the past. By and again. Fifty million years from now, For example, aluminum is used to produce
studying rocks, we can reconstruct the nothing will be as we now know it—not beverage cans; copper is used in electric
history of the Earth. Even the most the Andes, nor the Himalayas, nor the ice cables; and titanium, mixed with other
insignificant rocks can tell stories about of Antarctica, nor the Sahara Desert. durable metals, is used in the construction
other times, because rocks have been Weathering and erosion, though slow, will of spacecraft. We invite you to enjoy this
around since the beginning of the universe. never stop. This should free us from any book. It is full of interesting and worthwhile
They were part of the cloud of dust and illusion of the immortality of the Earth's information. Don't miss out on it!
gases that revolved around the Sun over features. What will everything be like in
four billion years ago. Rocks have been the future? We don't know. The only sure

8. Dynamics of the Earth's Crust MOUNTAINS OF SAND
Corkscrew Canyon in Arizona
contains an array of shapes, colors,
and textures. The sand varies from
pink to yellow to red depending on
TRAVERSING TIME 8-11
UNDER CONSTRUCTION 12-13
A CHANGING SURFACE 14-15
the sunlight it receives.
BEFORE ROCK, MINERAL 16-17
T
he Earth is like a blender in weathering and erosion by wind and rain sediment that eventually become
which rocks are moved around, wear down and transform the rock. This sedimentary rock. This rock cycle never
broken, and crumbled. The produces mountains, cliffs, and sand stops. In 50 million years, no single
fragments are deposited, dunes, among other features. The mountain we know will exist in the same
forming different layers. Then deposited material settles into layers of condition as it does today.

9. 8 DYNAMICS OF THE EARTH’S CRUST ROCKS AND MINERALS 9
Traversing Time 2 COLLISION
AND FUSION
Heavy elements
migrate.
3 METALLIC CORE
The light elements
form the mantle.
eologists and paleontologists use many sources to reconstruct
G the Earth's history. The analysis of rocks, minerals, and fossils
found on the Earth's surface provides data about the
deepest layers of the planet's crust and reveals both climatic and
atmospheric changes that are often associated with
catastrophes. Craters caused by the impact of meteorites and THE CORE
The Earth's core is
other bodies on the surface of the Earth also reveal valuable
information about the history of the planet.
extremely hot and
is made mostly of
iron and nickel.
Mountains
are external folds of the crust
produced by extremely powerful
forces occurring inside the Earth.
Complex
The region that will The fragments of
Structure
THE FORMATION OF THE INTERIOR
Cosmic materials began to
1 become North America
moves toward the
Equator, thus initiating
continents combine to
form a single continent
called Pangea.
accumulate, forming a growing celestial
Small bodies and
dust accumulate
542 OROGENIES the development of the
body, the precursor of the Earth. High to become the size The supercontinent Geological history recognizes long periods (lasting most important The Appalachian
temperatures combined with gravity of an asteroid. Panotia forms, containing millions of years) of intense mountain formation carboniferous formations. Mountains form.
caused the heaviest elements to portions of present-day called orogenies. Each orogeny is characterized by Gondwana moves slowly; The formation of slate
migrate to the center of the planet continents. North America its own particular materials and location. the ocean floor spreads through sedimentation is
and the lighter ones to move toward separates from Panotia. at a similar speed. at its peak.
the surface. Under a rain of meteors, The oldest 1,100 The first major Laurentia and
the external layers began to minerals, such as Rodinia, an early orogeny Baltica converge, Baltica and Siberia
consolidate and form the Earth's crust. zircon, form. supercontinent, (Caledonian creating the clash, forming the Ural
In the center, metals such as iron forms. folding) begins. Caledonian range. Mountains.
concentrated into a red-hot nucleus. The oldest rocks Gondwana moves Gneiss forms on
metamorphose, A meteorite falls in toward the South the coast of Eruptions of basalt
forming gneiss. Sudbury, Ontario, Pole. Scotland. occur in Siberia.
Canada.
Age in millions
of years 4,600 2,500 542 488.3 443.7 416 359.2 299
ERA Hadean Proterozoic Paleozoic THE ERA OF PRIMITIVE LIFE
PERIOD Pregeologic Precambrian Cambrian Ordovician Silurian Devonian Carboniferous Permian
EPOCH
Climate
Consolidation The Earth cools 2,500 Temperatures fall. It is thought that the By this period, Temperatures were Hot, humid climates The largest carbon
begins under a and the first The level of carbon Earth's atmosphere vertebrates with typically warmer than produce exuberant deposits we observe
Glaciations: White Earth
rain of meteors. ocean is formed. dioxide (CO2) in the contained far less carbon mandibles, such today, and oxygen forests in today form where
The Earth undergoes the first of its
atmosphere is 16 dioxide during the as the placoderms, (O2) levels attained swamplands. forests previously
massive global cooling events
times higher than it Ordovician than today. osteichthyans their maximum. existed.
ELEMENTS PRESENT ACCORDING TO THE TABLE (glaciations).
is today. Temperatures fluctuate (bony fish), and
Existing in different combinations, the crust of the Earth within a range similar to acanthodians,
O
contains the same elements today as those that were
present when the planet was formed. The most abundant
46.6% 800 Second glaciation what we experience
today.
have already
emerged.
element in the crust is oxygen, which bonds with metals Si
Metals
Transition metals
600 Last massive glaciation
and nonmetals to form different compounds. 27.7%
Nonmetals
Life Noble gases
THE FIRST ANIMALS THE CAMBRIAN EXPLOSION SILURIAN Amphibians diversify Palm trees and
Mg Lanthanide series
Ca Among the most mysterious fossils of the Fossils from this time attest to One of the first and reptiles originate conifers replace the
2.1% Actinide series
3.6% the great diversity of marine pisciform vertebrates, from one amphibian vegetation from the
Na Precambrian Period are the remains of the
Al an armored fish
K 2.8% Fe 8.1% Ediacaran fauna, the Earth's first-known animals and the emergence group to become the Carboniferous Period.
without mandibles
2.6% 5.0% animals. They lived at the bottom of the of different types of first amniotes. Winged
ocean. Many were round and reminiscent of skeletal structures, such insects such as MASS EXTINCTION
as those found in sponges The rocks of this period dragonflies emerge. Near the end of the
jellyfish, while others were flat and sheetlike.
and trilobites. contain an abundance Permian Period, an
of fish fossils. estimated 95 percent of
TRILOBITES marine organisms and over
Marine arthropods Areas of solid ground two thirds of terrestrial
with mineralized are populated by ones perish in the greatest
exoskeletons gigantic ferns. known mass extinction.

10. 10 DYNAMICS OF THE EARTH’S CRUST ROCKS AND MINERALS 11
IMPACT FROM THE OUTSIDE The heat caused by the
It is believed that a large meteor fell on
Chicxulub, on the Yucatán Peninsula
(Mexico), about 65 million years ago. The
expansion of fragments
from the impact together
with the greenhouse effect
Elements in CRUST
The Earth's crust can reach
impact caused an explosion that created a
cloud of ash mixed with carbon rocks. When
the debris fell back to Earth, some experts
brought about by the
spreading of ashes in the
stratosphere provoked a
Equilibrium a thickness of up to 6 miles
(10 km) at the bottom of the
ocean and up to 30 miles
(50 km) on the continents.
believe it caused a great global fire. series of climatic changes. Minerals, such as iron and silicates, are
It is believed that this widely spread among the major constituents
process resulted in the of the crust. Only the movements of the
62 miles extinction of the dinosaurs. crust on the molten mantle disrupt their
equilibrium.
(100 km)
The diameter of the crater produced by
North America and LITHOSPHERE
the impact of the meteor on the Yucatán The solid rock coating
Europe drift apart.
Peninsula. It is now buried under almost of the Earth, which
North and South
2 miles (3 km) of limestone. includes the exterior of
America are joined at the mantle
the end of this time
period. The formation of MANTLE
Patagonia concludes, The mantle is 1,800 miles
and an important (2,900 km) thick and is
overthrust raises the composed mainly of solid
rock. Its temperature
Andes mountain range. increases with depth. A
notable component of the
upper mantle is the
asthenosphere, which is
FORMATION OF semisolid. In the asthenosphere,
MOUNTAIN CHAINS superficial rock layers that will
Gondwana eventually form the Earth's
reappears.
60 Central Rocky Mountains crust are melted.
30 Alps
Africa separates 20 Himalayas The African Rift Zone and
from South America, the Red Sea open up. The
and the South Atlantic Indian protocontinent
Ocean appears. collides with Eurasia.
251
Mesozoic
199.6
THE ERA OF REPTILES
145.5 65.5
Cenozoic THE AGE OF MAMMALS
23.03
Triassic Jurassic Cretaceous Paleogene Neogene
Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Holocene
THE AGE OF FLOWERING PLANTS CORE
The level of oxygen At the end of the Cretaceous Period, THE LAST GLACIATION Outer Core
Carbon dioxide The global Temperatures drop The outer core is 1,400
(O2) in the the first angiosperms—plants with The most recent period of
levels increase. average to levels similar to miles (2,270 km) thick
atmosphere is much protected seeds, flowers, and glaciation begins three million years
Average temperature is those of today. The and contains melted iron,
lower than today. fruits—appear. ago and intensifies at the beginning nickel, and other minor
temperatures at least 62° F lower temperatures
of the Quaternary period. North chemical compounds.
are higher than (17° C). The ice cause forests to
Pole glaciers advance, and much of
today. layer covering shrink and grasslands Inner Core
the Northern Hemisphere becomes The inner core has a diameter of
Antarctica later to expand.
covered in ice. 756 miles (1,216 km). It is made of
thickens.
iron and nickel, which are solidified
due to their exposure to high
pressure and temperature conditions.
Vast development
ANOTHER MASS EXTINCTION of feathered bird HUMAN BEINGS APPEAR ON EARTH.
Proliferation of Birds emerge. Toward the end of the Cretaceous species and Although the oldest hominid fossils
insects Period, about 50 percent of existing mammals covered (Sahelanthropus) date back to seven million
The dinosaurs species disappear. The dinosaurs, the with long fur years ago, it is believed that modern humans
Appearance of undergo adaptive large marine reptiles (such as the emerged in Africa at the end of the
dinosaurs radiation. Plesiosaurs), the flying creatures of that Pleistocene. Humans migrated to Europe
period (such as the Pterosaurs), and the 100,000 years ago, although settling there
ammonites (cephalopod mollusks) was difficult because of the glacial climate.
The first mammals ALLOSAURUS disappear from the Earth. At the MAMMOTHS According to one hypothesis, our ancestors
evolve from a group This carnivore beginning of the Cenozoic Era, most of Mammoths lived in Siberia. reached the American continent about
of reptiles called measured 39 feet the habitats of these extinct species The cause of their extinction 10,000 years ago by traveling across the
Therapsida. (12 m) long. begin to be occupied by mammals. is still under debate. area now known as the Bering Strait.

11. 12 DYNAMICS OF THE EARTH’S CRUST ROCKS AND MINERALS 13
Under Construction KILAUEA CRATER
Hawaii
ur planet is not a dead body, complete and unchanging. It is an ever-changing system whose
O activity we experience all the time: volcanoes erupt, earthquakes occur, and new rocks
emerge on the Earth's surface. All these phenomena, which originate in the interior of the
planet, are studied in a branch of geology called internal geodynamics. This science analyzes
Latitude 19° N
Longitude 155° W
processes, such as continental drift and isostatic movement, which originate with the
movement of the crust and result in the raising and sinking of large areas. The
movement of the Earth's crust also generates the conditions that form new rocks.
This movement affects magmatism (the melting of materials that solidify
to become igneous rocks) and metamorphism (the series of
transformations occurring in solid materials that give rise to
metamorphic rocks).
Magmatism Metamorphism Folding Fracture
Magma is produced when the temperature in the mantle or crust reaches a level at An increase in pressure and/or temperature causes Although solid, the materials forming the Earth's When the forces acting upon rocks become too intense,
which minerals with the lowest fusion point begin to melt. Because magma is less rocks to become plastic and their minerals to crust are elastic. The powerful forces of the Earth the rocks lose their plasticity and break, creating two
dense than the solid material surrounding it, it rises, and in so doing it cools and begins to become unstable. These rocks then chemically react with place stress upon the materials and create folds in the types of fractures: joints and faults. When this process happens
crystallize. When this process occurs in the interior of the crust, plutonic or intrusive the substances surrounding them, creating different rock. When this happens, the ground rises and sinks. When too abruptly, earthquakes occur. Joints are fissures and cracks,
rocks, such as granite, are produced. If this process takes place on the outside, volcanic chemical combinations and thus causing new rocks to this activity occurs on a large scale, it can create mountain whereas faults are fractures in which blocks are displaced
or effusive rocks, such as basalt, are formed. form. These rocks are called metamorphic rocks. Examples ranges or chains. This activity typically occurs in the parallel to a fracture plane.
of this type of rock are marble, quartzite, and gneiss. subduction zones.
OUTER PRESSURE TEMPERATURE FOLDS RUPTURE
CRUST This force gives rise to new High temperatures make For folds to form, rocks When rocks
Volcanic Crust metamorphic rocks, as older the rocks plastic and must be relatively rupture quickly, an
rocks rocks fuse with the minerals their minerals unstable. plastic and be acted earthquake occurs.
Sea that surround them. upon by a force.
Oceanic Level
Plate
Zone of
62 miles Subduction
INNER
CRUST Magmatic (100 km)
Plutonic Chamber
Rocks 124 miles
Convective (200 km)
Currents
Asthenosphere

12. 14 DYNAMICS OF THE EARTH’S CRUST ROCKS AND MINERALS 15
A Changing Surface CORKSCREW
he molding of the Earth's crust is the product of two great destructive forces: weathering and CANYON
T erosion. Through the combination of these processes, rocks merge, disintegrate, and join
again. Living organisms, especially plant roots and digging animals, cooperate with
these geologic processes. Once the structure of the minerals
Arizona
Latitude 36° 30´ N
Longitude 111° 24´ W
that make up a rock is disrupted, the minerals
disintegrate and fall to the mercy of the
rain and wind, which erode them.
Water
current
Erosion Weathering CHEMICAL
External agents, such as water, wind, air, and living Mechanical agents can disintegrate rocks, and PROCESSES
beings, either acting separately or together, wear The mineral components
chemical agents can decompose them. Disintegration of rocks are altered.
down, and their loose fragments may be transported. and decomposition can result from the actions of plant They either become new
This process is known as erosion. In dry regions, the roots, heat, cold, wind, and acid rain. The breaking down of minerals or are released
wind transports grains of sand that strike and rock is a slow but inexorable process. in solution.
polish exposed rocks. On the coast, wave River
Cave
action slowly eats away at the rocks.
MECHANICAL PROCESSES Limestone
TEMPERATURE
A variety of forces can cause rock When the temperature of the
fragments to break into smaller air changes significantly over a
pieces, either by acting on the rocks few hours, it causes rocks to
Wind directly or by transporting rock expand and contract abruptly. Transportation and
fragments that chip away at the rock
surface.
The daily repetition of this
phenomenon can cause rocks
Sedimentation
to rupture. In this process, materials
EOLIAN HYDROLOGIC PROCESSES eroded by the wind or water
All types of moving water slowly wear are carried away and
PROCESSES down rock surfaces and carry loose deposited at lower elevations,
The wind drags small particles
particles away. The size of the particles that WATER and these new deposits can
against the rocks. This wears them
are carried away from the rock surface In a liquid or frozen state, later turn into other rocks.
down and produces new deposits
depends on the volume and speed of the water penetrates into the
of either loess or sand depending
flowing water. High-volume and high- rock fissures, causing them
on the size of the particle.
velocity water can move larger particles. to expand and shatter.

13. 16 DYNAMICS OF THE EARTH’S CRUST ROCKS AND MINERALS 17
Before Rock, Mineral
he planet on which we live can be seen as a large rock or, more precisely, as a From Minerals to Rocks
T large sphere composed of many types of rocks. These rocks are composed of
tiny fragments of one or more materials. These materials are minerals, which
result from the interaction of different chemical elements, each of which is stable
From a chemical perspective, a mineral is a
homogeneous substance. A rock, on the other
hand, is composed of different chemical substances,
which, in turn, are components of minerals. The
QUARTZ
Composed of silica,
quartz gives rock a
white color.
only under specific conditions of pressure and temperature. Both rocks and mineral components of rocks are also those of
mountains. Thus, according to this perspective, it is
minerals are studied in the branches of geology possible to distinguish between rocks and minerals.
called petrology and mineralogy.
MICA
Composed of
thin, shiny
sheets of silicon,
aluminum, potassium,
12 millionago
and other minerals, mica
can be black or colorless.
years GRANITE
Rock composed of
FELDSPAR
A light-colored
feldspar, quartz, and silicate, feldspar
rock batholiths formed during a mica makes up a large
period of great volcanic activity part of the crust.
and created the Torres del Paine
and its high mountains.
TORRES DEL PAINE
Chilean Patagonia
Latitude 52° 20´ S
Longitude 71° 55´ W
Composition Granite
Highest summit Paine Grande (10,000 feet [3,050 m])
CHANGE OF STATE
Surface 598 acres (242 ha)
Temperature and pressure play a prominent part in rock
transformation. Inside the Earth, liquid magma is produced.
Torres del Paine National Park is located in Chile When it reaches the surface, it solidifies. A similar process
between the massif of the Andes and the Patagonian happens to water when it freezes upon reaching 32° F (0° C).
steppes.

14. Minerals DALLOL VOLCANO
Located in Ethiopia, Dallol is the only non-
oceanic volcano on Earth below sea level,
making it one of the hottest places on the
planet. Sulfur and other minerals that spring
YOU ARE WHAT YOU HAVE 20-21
A QUESTION OF STYLE 22-23
HOW TO RECOGNIZE MINERALS 24-25
CRYSTALLINE SYMMETRY 30-31
PRECIOUS CRYSTALS 32-33
DIAMONDS IN HISTORY 34-35
from this volcano create very vivid colors. THE MOST COMMON MINERALS 36-37
A DESERT OF MINERALS 26-27
THE ESSENCE OF CRYSTALS 28-29 THE NONSILICATES 38-39
Graphite, for instance, is used to
D
allol is basically a desert of shades of orange. Some minerals Did you know it took human beings
minerals whose ivory- belong to a very special class. thousands of years to separate metal make pencils; gypsum is used in
colored crust is scattered Known as gems, they are sought and from rock? Did you also know that construction; and halite, also known
with green ponds and hoarded for their great beauty. The certain nonmetallic minerals are as salt, is used in cooking.
towers of sulfur salts in most valuable gems are diamonds. valued for their usefulness?

15. 20 MINERALS ROCKS AND MINERALS 21
You Are What You Have Polymorphism
inerals are the “bricks” of materials that make up the
M Earth and all other solid bodies in the universe. They are
usually defined both by their chemical composition and by
their orderly internal structure. Most are solid crystalline
A phenomenon in which the same
chemical composition can create
multiple structures and, consequently,
result in the creation of several different
minerals. The transition of one
substances. However, some minerals have a disordered internal polymorphous variant into another,
facilitated by temperature or pressure
structure and are simply amorphous solids similar to glass. conditions, can be fast or slow and either
Studying minerals helps us to understand the origin of the Earth. reversible or irreversible.
Minerals are classified according to their composition and
internal structure, as well as by the properties of hardness,
weight, color, luster, and transparency. Although more than Chemical Crystallization Mineral
4,000 minerals have been discovered, only about 30 are Composition System
common on the Earth's surface. CaCO3 Trigonal Calcite
CaCO3 Rhombic Aragonite
FeS2 Cubic Pyrite
Components MINERALS
COME FROM
FeS2 Rhombic Marcasite
The basic components of minerals are the
chemical elements listed on the periodic
table. Minerals are classified as native if they are
found in isolation, contain only one element, and
occur in their purest state. On the other hand, they
112
elements
C
C
Cubic
Hexagonal
Diamond
Graphite
are classified as compound if they are composed of listed in the
two or more elements. Most minerals fall into the periodic table.
compound category.
DIAMOND AND GRAPHITE
A mineral's internal structure influences its hardness. Both
1 NATIVE MINERALS graphite and diamond are composed only of carbon; however,
These minerals are classified into: they have different degrees of hardness.
A- METALS AND INTERMETALS
Native minerals have high thermal and electrical
Diamond Graphite
conductivity, a typically metallic luster, low
hardness, ductility, and malleability. They are easy
to identify and include gold, copper, and lead.
GOLD SILVER
An excellent thermal and electrical conductor. The close-up
Acids have little or no effect on it. image shows the
MORE THAN
dendrites formed by
the stacking of
octahedrons, sometimes in
an elongated form.
Microphotograph of
4,000 types of
minerals
have been recognized by the Carbon
silver crystal dendrites International Association of Mineralogy. Atom
2 COMPOUND
MINERALS
Isotypic Minerals
Compound minerals Isomorphism happens when minerals with the same structure, such as halite and galena,
are created when exchange cations. The structure remains the same, but the resulting substance is different,
chemical bonds form because one ion has been exchanged for another. An example of this process is siderite (rhombic
B- SEMIMETALS C- NONMETALS HALITE
between atoms of FeCO3), which gradually changes to magnesite (MgCO3) when it trades its iron (Fe) for similarly-
Native minerals that are more An important group of is composed of
fragile than metals and have minerals, which includes more than one element. sized magnesium (Mg). Because the ions are the same size, the structure remains unchanged. Model demonstrating
chlorine and sodium.
a lower conductivity. sulfur The properties of a how one atom bonds
Examples are arsenic, compound mineral differ to the other four
antimony, and bismuth. from those of its HALITE AND GALENA
constituent elements. Halite NaCl Galena PbS Each atom is joined to four other Atoms form hexagons that
Cl Na S Pb atoms of the same type. The are strongly interconnected
BISMUTH SULFUR carbon network extends in three in parallel sheets. This
dimensions by means of strong structure allows the sheets
covalent bonds. This provides the to slide over one another.
mineral with an almost
unbreakable hardness.
Cubic Internal Hardness of 10 Hardness of 1
Structure on the Mohs scale on the Mohs scale