Encyclopedia of Global Resources part 76 doc

Then, moving outward, come the outer core, the lower mantle, the upper mantle, and the Earth’s crust.. Roberts See also: Earth’s crust; Igneous processes, rocks, and mineral deposits; Ma

Obtaining Lithium

Lithium chloride is obtained by treating either

lith-ium hydroxide or lithlith-ium carbonate with hydrochloric

acid Chemists obtain pure metallic lithium by passing

electricity through molten lithium chloride or through

solutions of lithium chloride in ethanol or acetone in

low-carbon steel cells having graphite anodes

Uses of Lithium

Lithium is used to make batteries found in electric

meters, cameras, and other electronic equipment,

and lithium compounds have numerous practical

ap-plications Lithium carbonate and lithium borate are

used in the ceramic industry as glaze constituents,

while lithium perchlorate is a powerful oxidizing

agent used in solid fuel for rockets Lithium hydride, a

powerful reducing agent, is used in fuel cells, as a

shielding material for thermal neutrons emitted from

nuclear reactors, and to inflate lifeboats and air

bal-loons Lithium fluoride is used in infrared

spectrome-ters and as a flux in ceramics, brazing, and welding

Lithium chloride, the most common lithium salt, is

used to increase the conductivity of electrolytes in

low-temperature dry-cell batteries, as a dehumidifying

agent in air-conditioners, and in metallurgical

appli-cations Lithium is combined with aluminum and

magnesium to produce structural alloys;

lithium-mag-nesium alloys have the highest strength-to-weight

ra-tio of all structural materials In medicine, lithium

amide is important in the synthesis of antihistamines,

and lithium carbonate is used as a drug to treat a form

of mental illness known as bipolar affective disorder

(or manic-depressive disorder)

Alvin K Benson

Web Sites

Natural Resources Canada

Canadian Minerals Yearbook, 2005: Lithium

http://www.nrcan-rncan.gc.ca/mms-smm/busi-indu/cmy-amc/content/2005/35.pdf

U.S Geological Survey

Minerals Information: Lithium Statistics and

Information

http://minerals.usgs.gov/minerals/pubs/

commodity/lithium/

See also: Aluminum; Carbonate minerals; Ceramics;

Fuel cells; Glass; Magnesium; Nuclear energy;

Rub-ber, natural

Lithosphere

Category: Geological processes and formations

The usable mineral resources of the Earth are all within the lithosphere, and knowledge of its properties

is particularly important in the search for gas and oil.

Definition

The lithosphere (“stone sphere,” from Greek lithos)

consists of the outer, brittle portions of the Earth, in-cluding the upper mantle and crust

Overview The interior of the Earth has a number of layers, or concentric spheres At the center of the Earth is the inner core Then, moving outward, come the outer core, the lower mantle, the upper mantle, and the Earth’s crust Scientists subdivide the upper mantle into the asthenosphere, a partially molten zone, and, above that, the lithosphere The lithosphere, then, is the rigid (or brittle) outer shell of the Earth, which ex-tends to a depth of between 70 and 100 kilometers and rests on the asthenoshere It includes the Earth’s crust and part of the upper mantle

The upper mantle is approximately 700 kilometers thick The asthenosphere begins at a depth of approx-imately 70 to 100 kilometers and shows a rapid in-crease in density and a temperature in excess of 1,000° Celsius The asthenosphere is partially molten ultramafic material Because of its partially molten properties, the asthenosphere probably exhibits plas-tic flow Above the asthenoshere, the upper brittle portion of the upper mantle that is part of the litho-sphere is a dense ultramafic material that directly un-derlies the Earth’s crust The lithosphere comprises seven to ten major lithospheric “plates” that move slowly as they rest on the asthenosphere Plate tecton-ics refers to the movement of these plates and the land and ocean forms that are created as a result

Within the lithosphere, the boundary between the upper mantle and the crust is called the Mohorovi5i6 discontinuity, or Moho, which marks a compositional change in the rock The earth’s crust contains two ba-sic types of crustal material, oceanic and continental, with an average density of 2.9 and 2.6, respectively Oceanic crust ranges from 5 to 10 kilometers thick and is thinnest over seafloor-spreading areas Oceanic crust is primarily composed of dense basaltic rock

with a thin veneer of silt and carbonate precipitates;

however, a variety of minerals have been observed at

seafloor vents Continental crust is primarily

com-posed of felsic granitic rock, which is less dense than

oceanic crust; however, continental crust also includes

sedimentary and metamorphic rock and even

up-lifted oceanic basalt A variety of minerals of varying

economic importance occur in the continental crust

The continental crust averages 30 to 40 kilometers in

thickness, but it may be more than 70 kilometers thick

in some mountain areas

Oceanic crust is less dense than the parent mantle

material This is probably attributable to partial

melt-ing and crystal fractionation Felsic minerals have a

lower melting temperature than mafic minerals, and

mafic minerals are the first to crystallize out of a melt

As oceanic crust subducts below continental crust, the

subducting plate eventually melts, and its upwelling

liquid fraction produces less mafic intermediates

The lithosphere is highly variable, according to

re-gional studies In parts of the middle United States

and in the Gulf of Mexico region, for example, the

crust has thick sedimentary layers Oil companies

were able to measure the seismic wave patterns

gener-ated by many controlled explosions and discover

pe-troleum and natural gas within these layers The later

discovery of oil in northern Alaska was prompted by

the similarity of the crust there to the crust of these

re-gions As the study of the characteristics of the

litho-sphere—including plate tectonics—continues,

scien-tists will increasingly be able to use their knowledge to discover sites of mineral resources

Raymond U Roberts

See also: Earth’s crust; Igneous processes, rocks, and mineral deposits; Magma crystallization; Marine vents; Metamorphic processes, rocks, and mineral deposits; Plate tectonics; Plutonic rocks and mineral deposits; Seafloor spreading; Sedimentary processes, rocks, and mineral deposits; Volcanoes

Livestock and animal husbandry

Category: Plant and animal resources

Animal husbandry refers to the management of domes-ticated animals such as beef or dairy cattle, sheep, goats, pigs, and chickens: livestock Such animals con-stitute a renewable resource providing humans with food, fiber, fuel, power, implements, and other benefits.

Background Effective animal husbandry requires an affinity for the animals being managed, skill in handling them, and knowledge of them and their environment Re-spect for animals is important to good management,

as is skill in handling to minimize injuries and stress to both animal and handler Knowledge is needed of

Moho

Mo

ho

Ocean

U p p e r m a n t l e

Oceanic crust Continental crust

Lithosphere (70-100 kilometers deep)

their nutrition, reproduction, and behavior as well as

the physical, biological, cultural, and economic

con-text in which they are managed While some inputs

(such as aberrant weather and governmental

regula-tions) are beyond the control of the producer, good

management will ensure the most efficient

productiv-ity from the available inputs

Intensive and Extensive Management

Intensive and extensive management are the two main

options for animal husbandry Intensive management

refers to confinement-type operations that provide

animals with shelter, food, and water It has been

called “landless” because it requires very little

prop-erty Examples include beef feedlots,

concentrate-based dairy farms, and confinement swine or poultry

operations In extensive systems, on the other hand,

the animals are provided with an area in which they

fend for themselves, finding their own food, water,

and shelter Examples are rangeland beef operations,

pasture-based dairying, and free-range poultry farms

In practice, animal husbandry often includes both

in-tensive and exin-tensive management

In the early twenty-first century, the U.S beef

in-dustry generally involved extensive operations for at

least the first year of life and an intensive phase just

prior to market; availability and prices of feed grains

may determine the extent to which intensive

manage-ment is practiced Dairy operations around the world

range from intensive to extensive—from no to

exclu-sive pasture, respectively Seasonal variation of

pas-ture may dictate when it is available and used Because

dairy cows must be milked two or three times a day,

dairy operations are never as extensive as some beef

operations, where the producer may have contact

with the animals no more than once a year

Intensive animal management generally requires

more management expertise, more capital

invest-ment, and more energy utilization Since the animal is

totally under control of the producer, all needs of the

animal must be provided The inevitably greater

con-centration of animals requires closer attention to

their housing and health The larger capital

invest-ment is attributable to facilities and equipinvest-ment More

energy utilization is needed to maintain temperature

and ventilation as well as to operate equipment

In-tensive management also places greater emphasis on

maximizing animal performance Because more

capi-tal and energy are used, effort is made to extend

ani-mal performance by genetics, nutrition, and other

management tools Intensive managment also requires more dependence on others for feed While some in-tensive livestock producers raise their own feedstuff, many do not They may depend on crop farmers within the region or half a world away Contemporary

Meat: Leading Producers, 2006

Metric Tons

Beef and veal

Pork

European Union 21,677,000

Poultry

Source: U.S Department of Agriculture, National Agricultural Statistics Service, Agricultural Statistics,

2007.

swine operations in Japan and Korea require corn and

soybeans from the U.S Midwest

Extensive animal management demands more land

and more dependence on the animals’ abilities than

intensive management The larger land requirement

is a primary feature of this system The greater

depen-dence on the animals’ abilities follows from less direct

provision by the producer for their needs Survival

and growth may depend on their locating food, water,

and shelter as well as avoiding danger Reproduction

may be left to natural service, easy birthing, and good

mothering Extensive management involves more

tol-erance for decreased animal performance When

weather conditions do not provide sufficient food,

the animals will have less than maximal growth and

fertility Neonatal losses attributed to weather,

preda-tors, or terrain are tolerated Indeed, human

inter-vention may not be a realistic option when animals

are widely dispersed An important parameter is the

“stocking rate,” the number of animals per land area

Too few animals will not fully use the vegetation, as

many grasses are most nutritious at an early stage of

development and become less nutritious and coarser

if not eaten then Too many animals will overgraze,

impairing regrowth of the vegetation Optimum

“stocking rate” corresponds closely to the ecological

concept “carrying capacity,” the number of animals

that an area can sustain over an extended period

of time Extensive systems can demand substantial

management expertise For instance, pasture-based

dairying in New Zealand requires considerable

knowl-edge to optimize pasture growth and utilization

Biological and Nonbiological Parameters

Any animal management system must take into

ac-count numerous biological parameters pertinent to

the animal under management These include

nutri-tional requirements, biological time lag (time from

conception to market), reproduction (gestation

length and number of newborn, newborn survival),

efficiency of feed conversion, nature of weight gain,

genetic selection, and susceptibility to disease

Deci-sions are made about using natural service or artificial

insemination The extent to which agricultural

by-products, crop residues, and/or production

enhanc-ers are used depends on their efficacy, availability, and

price

Any animal management system also involves a

number of nonbiological parameters The available

climate, water supply, and land are physical attributes

that bear upon the husbandry options Two other fac-ets of the land affecting management are its tenure, whether owned, leased, or occupied, and its use, whether restricted or not Husbandry is also affected

by the availability and skill level of labor Another fac-tor is the infrastructure—the dependability of trans-portation providing access to markets, postfarm pro-cessing, and communication systems Profitability, the difference between receipts and cost of inputs, as well

as any subsidies, determines whether one can engage

in any agricultural activity for long Personal values, including lifestyle and risk management, also impact involvement in animal agriculture Finally, historical and societal values, particularly those directly touch-ing on the use of animals and natural resources, influ-ence the extent and nature of animal husbandry

Issues Three issues of contemporary interest relative to live-stock and animal husbandry concern the need for an-imal agriculture, its sustainability, and its increasing corporate nature The willingness of people to pur-chase and consume products of animal origin will al-ways determine the need for animal agriculture If the price people must pay for such products is too high, demand will decline As the general affluence of a country increases, the demand for foods of animal or-igin increases

The sustainability of contemporary agriculture has been called into question because of its heavy depen-dence on fossil fuels for energy and its adverse effects

on the environment Properly managed, animals have

a role to play in sustainable agriculture They can help dispose of some agribusiness by-products—crop resi-dues and crops not suitable for human consumption— and generate waste that can be used to fertilize crops Animal agriculture is increasingly conducted by corporations rather than by family-owned farms or ranches Once farming moves away from subsistence farming and generates excess over what the farm fam-ily needs, it becomes a business The pressure for effi-ciency, as well as for high and consistent product qual-ity, is driving animal agriculture toward increasingly specialized and integrated enterprises While this ten-dency appears to be inevitable, serious concerns arise concerning the oligopolies, if not monopolies, that may control the production of animal products and the management of domestic animals, a valued re-newable resource

James L Robinson

Further Reading

Campbell, John R., M Douglas Kenealy, and Karen L

Campbell Animal Sciences: The Biology, Care, and

Pro-duction of Domestic Animals 4th ed Boston:

McGraw-Hill, 2003

Campbell, Karen L., and John R Campbell

Compan-ion Animals: Their Biology, Care, Health, and

Manage-ment 2d ed Upper Saddle River, N.J.: Pearson

Prentice Hall, 2009

Cheeke, Peter R Contemporary Issues in Animal

Agricul-ture 2d ed Danville, Ill.: Interstate, 1999.

Ensminger, M Eugene The Stockman’s Handbook 7th

ed Danville, Ill.: Interstate, 1992

Field, Thomas G., and Robert E Taylor Scientific Farm

Animal Production: An Introduction to Animal Science.

9th ed Upper Saddle River, N.J.: Prentice Hall,

2008

Gillespie, James R., and Frank Flanders Modern

Live-stock and Poultry Production 8th ed Clifton Park,

N.Y.: Delmar Cengage Learning, 2009

Shapiro, Leland Introduction to Animal Science Upper

Saddle River, N.J.: Prentice Hall, 2001

Web Site

U.S Department of Agriculture

Animal Production

http://www.usda.gov/wps/portal/!ut/p/_s.7_0_A/

7_0_1OB?navid=ANIMAL_PRODUCTION&pare

ntnav=AGRICULTURE&navtype=RT

See also: Animal breeding; Animal domestication;

Animal power; Farmland; Overgrazing; Rangeland

Logging See Clear-cutting; Timber

industry; Wood and timber

Los Angeles Aqueduct

Categories: Historical events and movements;

obtaining and using resources

Construction of the Los Angeles Aqueduct generated

considerable controversy; ultimately the aqueduct

en-abled Los Angeles to expand by taking water from

sources in central California.

Definition The Los Angeles Aqueduct is a 544-kilometer-long sys-tem that transports water from the Owens Valley and Mono Basin east of the Sierra Nevada south to the Los Angeles metropolitan area The original aqueduct was proposed in the early 1900’s as a means of supply-ing the growsupply-ing Los Angeles region with an enlarged and reliable water source for the twentieth century The original aqueduct was completed in 1913 and its extension was completed in 1941 A second aqueduct was completed in 1970

Overview Los Angeles’ Department of Water and Power, under the leadership of William Mulholland and with the help of former Los Angeles mayor Fred Eaton, ob-tained the water rights to the Owens River by purchas-ing more than 97,000 hectares of land in Inyo County Much of the population of the prosperous Owens Valley bitterly opposed the aqueduct but could not stop the construction once the water rights had been bought by the Los Angeles Department of Water and Power

The city sold bonds worth more than $24 million to fund the construction of the aqueduct down the Owens Valley, across part of the Mojave Desert, and into the Los Angeles basin Mulholland directed the construction of the mammoth project, which began

in 1907 and took five years to complete The entire

375 kilometers of the original aqueduct transports water by gravity flow and consists of more than 274 ki-lometers of open ditch, 19 kiki-lometers of steel siphons, and 142 tunnels that totaled 85 kilometers In addi-tion, the project required the construction of more than 800 kilometers of trails and roads, 190 kilome-ters of railroad tracks, and 272 kilomekilome-ters of transmis-sion lines The project was one of the greatest engi-neering accomplishments of the early twentieth century

In 1930, Los Angeles approved another $38 mil-lion to extend the aqueduct northward into the Mono Basin in order to tap rivers and streams that feed into Mono Lake The extension was completed in 1941, and waters were diverted into the aqueduct 544 kilo-meters north of the city The diversion of water from Mono Lake eventually caused the lake level to drop 14 meters and the salinity of the lake to rise Environ-mental groups went to court to halt the diversion of water, and lengthy litigation ensued As Los Angeles continued to grow, the city saw the expanded need for

more water from the eastern Sierra Nevada, and in

1963, it appropriated more money to build another

aqueduct from the Owens Valley This second

aque-duct was completed in 1970 and increased the total

amount of water that could be transported by about

50 percent to a total average capacity of 19 cubic

me-ters per second Much of the water for the second

aq-ueduct was to be groundwater pumped from the

Owens Valley However, the Los Angeles Department

of Water and Power has been restricted in their appro-priations by litigation brought by local residents and environmental groups

Jay R Yett

See also: Irrigation; Water rights; Water supply sys-tems

Maathai, Wangari

Category: People

Born: April 1, 1940; Ihithe village, Nyeri District,

Kenya

An environmental and social activist, Maathai

estab-lished the far-reaching Green Belt movement, a

grass-roots organization whose members have planted more

than thirty million trees since the group’s founding in

1977 Maathai received the Nobel Peace Prize in 2004

and helped launch the Billion Tree Campaign in

2006.

Biographical Background

Wangari Muta Maathai was born Wangari Muta on

April 1, 1940, in the village of Ihithe, Nyeri District of

Kenya, the daughter of subsistence farmers With the

help of scholarships, she was able to study in the

United States, where she earned bachelor’s and

mas-ter’s degrees in biological science She then returned

to Kenya to study anatomy at the University of

Nai-robi According to her memoir, Unbowed (2006), in

1971, she became the first woman in east and central

Africa to earn a Ph.D However, her progressive views

spurred criticism from male colleagues and

govern-ment officials These pressures strained her marriage

to Mwangi Mathai, with whom she had three children;

he eventually sued for divorce and demanded that she

change her surname In her memoir, Maathai

ex-plains that she chose instead to insert an extra “a,”

thus signifying her right to identify herself In 2004,

Maathai became the first African woman to win the

Nobel Peace Prize

Impact on Resource Use

Maathai’s inspiration had two sources: deforestation

and poverty Upon her return to Kenya from the

United States, she realized how much of her country’s

landscape had changed, as farmers were forced to cut

down increasingly more trees Maathai also was

deter-mined to help her husband keep his campaign

prom-ises to create jobs She created a business called

Envirocare, which hired people to raise tree seedlings

in nurseries for eventual planting throughout Kenya

The program faced many obstacles, but in 1977, Maathai gained the support of Kenya’s National Council of Women and renamed the endeavor the

Green Belt movement In The Green Belt Movement: Sharing the Approach and the Experience (1988, revised

2003), Maathai states that the organization’s “one person, one tree” motto dictated its goal of planting fifteen million trees, one for each person in Kenya By the early 2000’s, Maathai and other members of the movement had planted more than twice that number Maathai simultaneously continued to build her in-fluence in the environmental movement, campaign-ing vigorously against a planned skyscraper in Nai-robi’s Uhuru Park Although the government evicted the Green Belt movement from its offices in response

to the protest, the project was ultimately stopped

Wangari Maathai, winner of the 2004 Nobel Peace Prize, at the

2009 NAACP Image Awards (Getty Images)

Maathai similarly opposed the government’s attempts

to sell off valuable forestland to developers, shaming

prospective financiers into withdrawing their

sup-port In retaliation, Maathai was imprisoned several

times, but her growing stature in the international

community made detaining her without cause

in-creasingly difficult for the authorities

In 2002, Maathai won a seat in Kenya’s parliament

and was appointed as the assistant minister of the

En-vironment, Natural Resources, and Wildlife the

fol-lowing year After winning the Nobel Peace Prize in

2004, she helped the United Nations Environment

Programme launch the Billion Tree Campaign The

group’s target was reached more quickly than

ex-pected, and a new goal of planting seven billion trees

by the end of 2009 was established Although many

in-dividuals and organizations have contributed

signifi-cantly to reforestation efforts, Maathai has had a

pro-found influence on this issue

Amy Sisson

See also: Forests; Greenhouse gases and global

cli-mate change; Nobel, Alfred; Reforestation

McCormick, Cyrus Hall

Category: People

Born: February 15, 1809; Rockbridge County,

Virginia

Died: May 13, 1884; Chicago, Illinois

As inventor of the mechanical reaper, McCormick

transformed agriculture in the mid-nineteenth century

by streamlining the process of harvesting grain,

result-ing in dramatic increases in grain production and the

fueling of westward expansion.

Biographical Background

Cyrus Hall McCormick, the son of a prosperous

Vir-ginia farmer, developed the first successful

mechani-cal grain reaper in 1831 by improving upon a design

conceived by his father Sales of the reaper—which

was capable of cutting, threshing, and bundling up to

5 hectares of grain per day—grew slowly at first

de-spite successful early demonstrations of its ability

Westward expansion and the resultant demand for

greater grain yields increased interest in the

mechani-cal reaper during the late 1830’s In 1839, McCormick

formed a business partnership with his brothers and began mass-producing mechanical reapers in Chi-cago, the trade hub of the Midwest and western fron-tier With the aid of innovative marketing techniques and an increasing availability of railroad lines for ship-ping, McCormick sold large numbers of mechanical reapers, particularly in grain-producing Midwestern states and territories, during the 1840’s and 1850’s

Impact on Resource Use The McCormick reaper exerted an immediate and dramatic impact upon American agriculture, com-merce, and society during the mid-nineteenth cen-tury The reaper greatly decreased the cost of grain farming and increased grain yields per hectare, prompting farmers to produce more grain The in-crease in production helped meet the growing de-mand for foodstuffs resulting from population expan-sion in the eastern United States and transformed the United States into a major exporter of grain The reaper also contributed to American urbanization

Cyrus Hall McCormick invented the crop reaper that bears his name (Library of Congress)

and industrialization by reducing demand for

agricul-tural labor in rural areas, encouraging rural farm

workers to migrate to cities, and providing a growing

labor pool to meet the increased demand for

indus-trial workers in urban areas The production and

mar-keting of foodstuffs thus assumed a larger role in

busi-ness and industry as the number of food consumers

grew and the ranks of food producers diminished

Increasing urbanization prompted a growing

em-phasis upon transportation in the United States:

Fewer Americans produced their own food and their

proximity to food sources decreased, which fueled the

growth of railroads, roads, turnpikes, and trails

con-necting consumers to local and regional commercial

centers By increasing demand for farmland in

Mid-western states, the McCormick reaper became a

driv-ing force for westward expansion, producdriv-ing changes

in the American social and political landscape that

af-fected numerous issues surrounding resource use,

in-cluding conflicts with indigenous peoples over land

and resources, conflicts between livestock owners

over the use of grazing lands, and the escalating

de-bate over utilization of slave labor in the American

South

The McCormick reaper was the first of a number of

agricultural machines that collectively transformed

agriculture, commerce, and daily living during the

late nineteenth and early twentieth centuries The

mechanization of farming influenced a number of

so-cial and economic trends in the United States and

worldwide, including the development of highways,

the emergence of the petrochemical and agribusiness

industries, and mass migrations of farm laborers from

rural areas to cities These trends resulted in dramatic

changes in the production, delivery, utilization, and

allocation of resources

Michael H Burchett

See also: Agricultural products; Agriculture

indus-try; Mineral resource use, early history of; Population

growth; Transportation, energy use in; Wheat

Magma crystallization

Category: Geological processes and formations

Magma crystallization is a geologic process in which

molten magma in the Earth’s interior cools and

subse-quently crystallizes to form an igneous rock The crys-tallization process produces many different types of minerals, some of which are valuable natural re-sources.

Background Magma is molten rock material consisting of liquid, gas, and early-formed crystals It is hot (900° to 1,200° Celsius), mobile, and capable of penetrating into or through the Earth’s crust from the mantle, deep in the Earth’s interior Most magma cools in the Earth’s crust; in a process similar to ice crystallizing from water as the temperature drops below the freezing point, minerals crystallize from molten magma to form a type of rock called igneous rock Once com-pletely crystallized, the body of igneous rock is called

an intrusion Some magma, however, works its way to the surface and is extruded as lava from volcanoes

Mineral Growth Magma that remains below the surface cools at a slow rate Ions have time to collect and organize them-selves into orderly, crystalline structures to form min-erals These minerals grow larger with time and, if the cooling rate is slow enough, may grow to several centi-meters in diameter or larger Igneous rocks with min-erals of this size are said to have a phaneritic texture Magma that reaches the surface, on the other hand, cools very rapidly and forms rocks that consist of ex-tremely fine-grained minerals or quenched glass These rocks have an aphanitic or glassy texture Con-sequently, it is those minerals which grow beneath the surface that reach sizes large enough to be considered economically feasible resources

Concentration of Valuable Elements Minerals do not crystallize from magma all at once Instead, they follow a sequence of crystallization as the temperature decreases In general, silicate miner-als (substances with silicon-oxygen compounds) with high contents of calcium, iron, and magnesium crys-tallize early, followed by silicate minerals with high contents of aluminum, potassium, and sodium Ex-cess silica crystallizes last as the mineral quartz Bonding factors such as ionic size and charge prevent some elements from incorporation into early crystal-lizing minerals Thus they are more highly concen-trated in the residual magma and become incorpo-rated into the last minerals to crystallize, forming rocks called granites and pegmatites These rocks may

contain minerals such as beryl, spodumene,

lepido-lite, and uraninite, which include important elements

such as beryllium, lithium, and uranium Granites

and pegmatites are also important sources for

feld-spar and sheet mica

Diamonds and Kimberlites

Perhaps the best-known magmatic minerals are

dia-monds Formed deep in the mantle at extremely high

temperatures and pressures, diamonds are carried

by a certain type of magma as it violently intrudes

upward through the crust, sometimes reaching the

surface Upon cooling and crystallizing, this magma

forms a pipe-shaped igneous rock known as

kim-berlite It is in kimberlites that most diamonds are

found Most kimberlite pipes are less than one square

kilometer in horizontal area, and they are often

grouped in clusters Most of the known

diamond-bearing kimberlite pipes are found in southern

Af-rica, western Australia, Siberia, and Canada

Magmatic Sulfide Deposits

Most major metals used in industry (copper, iron,

lead, nickel, zinc, and platinum) are found in sulfide

minerals, which are substances that contain

metal-sulfur compounds When magma is in the early stages

of cooling and crystallizing underground, certain

processes can cause droplets of liquid sulfide to form within it These sulfide droplets attract metallic cat-ions and concentrate them by factors ranging from

100 to 100,000 over their normal levels in the host magma The droplets eventually cool and solidify to form sulfide minerals such as pyrite (“fool’s gold”), galena (lead sulfide), and sphalerite (zinc sulfide) Sulfide minerals such as these become important tar-gets for mining because of their high concentration

of metals

Layered Magmatic Intrusions Some magmas give rise to layered intrusions in which

a specific sequence of minerals is repeated many times from bottom to top in a process called gravity layering (also called rhythmic layering) Dark-colored, heavier minerals such as pyroxene, olivine, and chro-mite concentrate near the base of each layer, grading

to predominantly light-colored minerals such as plagioclase at the top Each mineral sequence is a sep-arate layer, averaging several meters thick and rang-ing from less than 2 centimeters to more than 30 me-ters It has been suggested that the origin of gravity layering involves multiple injections of fresh magma into a crystallizing magma chamber, effectively re-plenishing the magma and allowing the same miner-als to crystallize repeatedly

The Bushveld intrusion in South Africa, one of the largest layered in-trusions, contains multiple gravity layers and is more than 7,000 meters

in total thickness Layered intrusions contain the Earth’s main reserves for chromium and platinum In the Bushveld intrusion, chromium oc-curs in the mineral chromite, and platinum in platinum-iron alloys, braggite, and other platinum-metal compounds The main source for platinum minerals in the Bushveld intrusion, and the source for ap-proximately half the Earth’s supply

of platinum, is the Merensky Reef, a layer of chromite and platinum min-erals 1 meter thick and more than

200 kilometers long Also present in the Bushveld intrusion is the min-eral magnetite, which yields impor-tant elements used in steel manufac-turing such as iron and vanadium

This example of igneous rock, the end result of magma crystallization, is found in Garrizo

Mountain in Arizona (USGS)