Mineral Resources China possesses deposits of all the discovered miner-als.. Other minerals that contain chromium include the gem-stones emerald and aquamarine, which owe their dis-tinct
Trang 1cubic meters, or almost equal to China’s total annual
runoff
In addition to fisheries and transportation,
irriga-tion, hydrairriga-tion, industrial, and numerous other uses,
water resources in China are a significant energy
re-serve The total hydrological power reserve is
esti-mated at 680 million kilowatts, ranking first in the
world Of the total, 380 million kilowatts can be
devel-oped to generate 1.9 trillion kilowatt-hours of
electric-ity, which contribute a great deal to China’s economic
development and the world economy
Climate Resources
China’s vast territory spans multiple climate zones
from the south to the north, including tropical,
sub-tropical, warm temperate, temperate, and boreal In
addition, the Qinghai-Tibet Plateau has a unique
al-pine region Nevertheless, the subtropical, warm
tem-perate, and temperate climate zones compose
ap-proximately 70 percent of the country As diverse as
the climate is, the basic characteristic is a continental
monsoon climate, which exhibits three main features:
substantial daily and seasonal temperature
differen-tial; uneven precipitation distribution, with a steady
drop from the southeast to the northwest by a
dra-matic 40:1 ratio; and dradra-matic wind turnover between
winter and summer During the winter, cold and dry
air from high latitude rises from the north In
sum-mer, warm and humid wind comes mainly from the
ocean in the southeast
The average annual temperatures in the eastern
re-gion descend from south to north, from 25° Celsius to
5.5° Celsius Most of the western Qinghai-Tibet Plateau
has annual average temperatures below 0° Celsius, but
the Tarim basin is 10° Celsius The temperature
differ-ential in the summer between the south and north is
small, only 10° Celsius In the winter, however, the
tem-perature difference between these two regions can be
as much as 50° Celsius The lowest temperature in the
Mohe area can dip below−50° Celsius The average
annual precipitation across China is 629 millimeters,
with a steady decline in annual precipitation from
southeast to northwest, which is somewhat similar to
the annual temperature patterns In general, high
precipitation is concentrated in the summer months
Based on the annual rainfall pattern, China’s areas
can be divided into 32 percent subhumid, 18 percent
semihumid, 19 percent semiarid, and 31 percent arid
The temperature and annual precipitation pattern
results in a concentrated distribution of agriculture in
central and southeast provinces and the Sichuan ba-sin, areas that are the foundation of China’s economy The vast territory in the northwest is not productive and contributes little to China’s agriculture
Biological Resources China is blessed with rich biological resources It has more wild animal species than any other country Ver-tebrates alone account for 5,200 species, 11 percent of the world’s total Of these animals, 499 species are mammals, 1,186 are birds, 376 are reptiles, 279 are amphibians, and 2,804 are fish This wildlife consists
of many endemic species, including some of the most well-known and rare animals: the giant panda, golden-haired monkey, Chinese alligator, crested ibis, white-lipped deer, South China tiger, red-crowned crane, brown-eared pheasant, and Yangtze River dol-phin (though this animal is thought to be extinct) The diverse flora in China includes twenty-five thousand species of seed plants From the tropical rain forests to the boreal coniferous forests, China has almost all the natural vegetation characteristic of the Northern Hemisphere The two hundred or so spe-cies of gymnosperms account for 25 percent of the world’s total In addition, there are seven thousand species of woody plants and twenty-nine hundred spe-cies of trees Several endemic plant spespe-cies are consid-ered as “living fossils,” including ginkgo, metasequoia, and golden pine
China has more than five thousand years of agricul-tural history, during which time the country has con-tributed many major crops important to humankind, including rice, soybeans, peaches, pears, plums, dates, grapefruit, lychees, and tea Based on their utiliza-tion, China has one thousand plant species for timber wood, three hundred starchy plants, more than ninety vegetable species, and six hundred oil species Its crops and germplasm continue to make vital contri-butions to the world’s economy
Mineral Resources China possesses deposits of all the discovered miner-als China’s total reserve of 146 mineral resources ranks the country third among world nations Coal, with a proved reserve of 877 billion metric tons, is found mainly in northern China, including the prov-inces of Shaanxi, Liaoning, Nei Monggol, and Hei-longjiang Among the 250 or so petroliferous basins identified, more than half of them (130) are under development
Trang 2The identified iron-ore reserves are estimated at 41
billion metric tons and distributed in multiple
gions China also ranks among leading nations in
re-serves of minerals such as tungsten, tin, antimony,
zinc, molybdenum, lead, and mercury China’s rare
earth reserves are more than the rest of the world’s
to-tal combined In fact, China accounts for 80 percent
of the world’s total reserves in that category The
diverse minerals and their large reserves provide
im-portant raw materials and energy sources that will
continue to power China’s economic growth and
de-velopment
In 1996, China established a thorough (although
not perfect) legal system for the exploration and
ex-ploitation of its minerals This system consists of many
laws, regulations, and rules promulgated by different
levels of government authorities On one hand, China
has encouraged foreign investment in mineral
re-sources exploration and new mining technologies
On the other hand, China imports minerals from
other countries and invests heavily in acquiring
min-eral resources abroad In 2008, China bought more
than half of Australia’s mineral exports China has
be-come the world’s largest consumer of raw materials
Energy Resources
China is rich in energy resources, but their
distribu-tion is uneven China ranks third among world
na-tions in energy reserves and output, with a total
en-ergy production equivalent to 11 billion metric tons
of standard coal In 2007, China’s coal output was 2.3
billion metric tons, which was top among countries;
its crude oil output was 172 million metric tons,
which ranked fifth; and its power generation capacity
was 720 gigawatts, which was fourth Gas production
reached 76 billion cubic meters in 2007
China relies heavily on coal for energy, but 80
per-cent of the coal reserves are conper-centrated in the
north The most economically developed eight
prov-inces south of the Chang River account for only 2
per-cent of the total coal reserves About 85 perper-cent of the
proved oil reserves are concentrated in the east
re-gion, north of the Chang Sixty-eight percent of
hy-draulic power developed is in the southwest region
China has addressed the low energy reserves in the
economically vibrant south through the construction
of nuclear power plants
The rapid economic growth and development that
began in 1982 have created an insatiable demand for
fossil fuel (oil and gas) that far exceeds China’s own
production capacity Thus, China became a major porter of oil beginning in the early 1990’s China im-ported 162 million metric tons of crude oil in 2007 A limit to China’s storage capacity is the only reason that figure is not higher That limit will soon change as China builds more strategic oil reserve facilities in the western region In short, China has become the world’s second largest energy user, trailing only the United States With an ever-increasing demand for oil, China is a driving force for energy consumption This in turn will have a significant impact on the world economy and environment
Other Resources China is a country rich in tourism resources Its vast territory and complex topography provide visitors to China with year-round opportunities The natural scenery in the north presents thousands of kilometers
of glaciers and snowy land during the winter The southern regions provide tourists with lush scenes of vegetation China’s exotic flora and fauna, found in its many national nature reserves, attract tourists of all ages China is dotted with magnificent rivers, lakes, mountains, and canyons Its long cultural history has produced numerous world-class attractions In addi-tion, the relatively low cost of travel and lodging, com-bined with the world’s burgeoning desire to know China, has fueled the powerful tourism engine in China
As one of the world’s four ancient civilizations, China is full of historical sites and cultural relics Some of the most famous attractions include the Great Wall, the Terracotta Army, Ming Tombs, Peking Man, and many other attractions of historical and cul-tural significance
Ming Y Zheng
Further Reading
Forney, Matthew “China’s Quest for Oil.” Time
(Octo-ber 18, 2004)
Lew, Alan A., and Lawrence Yu Tourism in China: Geo-graphic, Political, and Economic Perspectives Boulder,
Colo.: Westview Press, 1995
National Geographic Society National Geographic Atlas
of China Washington, D.C.: Author, 2007.
Sheehan, Peter Implications of China’s Rising Energy Use Singapore: World Scientific, 2008.
Xie, Jian, et al Addressing China’s Water Scarcity: Recom-mendations for Selected Water Resource Management Is-sues Washington, D.C.: World Bank, 2009.
Trang 3Zhang, Q., et al “Precipitation, Temperature, and
Runoff Analysis from 1950 to 2002 in the Yangtze
Basin, China.” Hydrological Sciences Journal 50, no 1
(2005): 65-80
Web Site
CIA World Factbook
https://www.cia.gov/library/publications/the-world-factbook/
See also: Agricultural products; Agriculture
indus-try; Ecozones and biogeographic realms; Energy
poli-tics; Hydrogen; Population growth; Three Gorges
Dam
Chlorites
Category: Mineral and other nonliving resources
Chlorites are most commonly found as microscopic
par-ticles in clays They are also found in metamorphic
rocks such as schists Metamorphic chlorites are
com-monly found in Michigan, Norway, the United
King-dom, and Japan Chlorites also occur in igneous rocks
as a product of biopyriboles that have been transformed
by heat and moisture They may also be found in
sedi-mentary rocks formed from pieces of older igneous or
metamorphic rocks containing chlorites.
Definition
The term “chlorite” (from the Greek word for “green”)
refers to a variety of hydrous aluminum silicates of
magnesium, iron, and other metals They are soft
green minerals with a glassy luster Chlorites are
brit-tle and can be ground into white or pale green
pow-der easily Thin sheets of chlorite are flexible but not
elastic
Chlorites are a group of silicate minerals consisting
of alternating layers of molecules forming two kinds
of two-dimensional sheets One layer consists of
sili-cate groups (one silicon atom bonded to four oxygen
atoms) bound to aluminum atoms, hydroxyl groups
(one oxygen atom bonded to one hydrogen atom),
and magnesium, iron, or other metallic atoms The
other layer consists of magnesium, iron, aluminum,
or other metallic atoms bound to hydroxyl groups If
most of the metallic atoms other than aluminum are
magnesium, the mineral is known as clinochlore If
the metallic atoms are iron, it is known as chamosite
If they are nickel, it is known as nimite If they are manganese, it is known as pennantite These four minerals are very similar
Overview Chlorites are most useful in the form of clay minerals They mix with other substances to form clays that are widely used in pottery and construction Clay miner-als are miner-also used in drilling “muds” (thick suspensions used to lubricate rotary drills) They may also be used
as catalysts in petroleum refining and to decolorize vegetable oils
The density of chlorite ranges from 2.6 to 3.3 grams per cubic centimeter On the Mohs scale, they have a hardness between 2 and 2.5; they are generally soft enough to be scratched with a fingernail
Chlorite usually exists as a microscopic component
of clay, along with organic material, quartz, and other minerals Visible pieces of chlorite may be found within a variety of rocks, particularly metamorphic rocks such as the very common schists
Chlorites are chemically similar to other clay min-erals (hydrous aluminum silicates) and are often found in combination with them They are generally more resistant to heat than other clay minerals are This fact is used to detect chlorite within clays A sam-ple of the clay is heated to between 500° and 700° Cel-sius, which breaks down the other clay minerals X-ray diffraction is then used to detect the layers of silicate chains that are characteristic of clay minerals If this pattern is detected, chlorite is present in the sample
In other regards chlorites have about the same prop-erties as other clay minerals
Rose Secrest
See also: Aluminum; Clays; Metamorphic processes, rocks, and mineral deposits; Silicates
Chromium
Category: Mineral and other nonliving resources
Where Found Chromium is a moderately abundant element that does not occur free in nature Its principal ore is known as chromite, (Fe,Mg) (Cr,Al)2O4 The world’s chromite resources are concentrated in the Eastern
Trang 4Hemisphere, with major producers including South
Africa, Kazakhstan, India, Zimbabwe, Turkey,
Fin-land, and Brazil
Primary Uses
Chromium is a strategic and critical resource used
principally in the production of alloys and
superal-loys, stainless steel, refractory materials, pigments,
and chemicals It is used for dyeing textiles and leather
tanning and as a laboratory glassware cleanser
Fur-thermore, chromium in its trivalent oxidation state is
an essential trace nutrient for humans and other
mammals
Technical Definition
Chromium (abbreviated Cr), atomic number 24, is a
metallic chemical element belonging to Group VIB of
the periodic table of the elements It has four
natu-rally occurring isotopes and an average molecular
weight of 51.996 Pure chromium is silver-gray, brittle,
and hard Its specific gravity is 7.19 at 20° Celsius, its
melting point is approximately 1,890° Celsius, and its
boiling point is 2,200° Celsius This lustrous metal will
take a high polish and does not tarnish in air In
chem-ical compounds chromium may have oxidation states
ranging from−2 to +6, but in most compounds it is
tri-valent (+3) or hexatri-valent (+6) The tritri-valent state is
more common in naturally occurring compounds,
while hexavalent chromium is frequently found in in-dustrial applications
Description, Distribution, and Forms Chromium is a commercially important metallic ele-ment Forming compounds with brilliant red, yellow, and green hues, it derives its name from the Greek
chroma (color) Its concentration in the lithosphere is
100 grams per metric ton Total world production of chromite is about 20 million metric tons Trivalent chromium, the form most often found in nature, is a trace element in the human body; by contrast, hexava-lent chromium is a highly toxic substance whose con-centrations in the environment are regulated by law Approximately 95 percent of the world’s chro-mium resources are found in southern Africa, with South Africa the leading producer in the region Other world producers include Kazakhstan, India, Turkey, Finland, Brazil, and Russia Chromium is present in a number of minerals, but chromite is its only commercial ore Primary deposits of chromite occur as stratiform and podiform ores found in cer-tain types of ultrabasic (low-silica) rocks Secondary alluvial deposits of chromite are formed by the weath-ering of stratiform (layered) and podiform ores Stratiform chromite deposits are often several me-ters thick, extend over large areas, have a relatively uni-form composition, and frequently include
Data from the U.S Geological Survey, U.S Government Printing Office, 2009.
3,300,000 3,700,000
9,600,000
Withheld
4,900,000
Metric Tons Gross Weight
10,500,000 9,000,000
7,500,000 6,000,000
4,500,000 3,000,000
1,500,000 United States
India
Kazkhstan
South Africa
Other countries
U.S data were withheld to avoid disclosure of company propriety data.
Note:
Chromium: World Mine Production, 2008
Trang 5bearing zones They formed as chromite crystallized
and precipitated from silicate melts Examples
in-clude the Bushveld Igneous Complex in Transvaal,
South Africa; the Great Dyke in Zimbabwe; and the
Stillwater Complex in Montana Stratiform deposits
constitute more than 90 percent of the world’s
identi-fied chromite reserves All the commercially
signifi-cant stratiform chromites are Precambrian in age and
occur in stable cratons, portions of the Earth’s crust
that have experienced little deformation over a long
period of geologic time
In podiform deposits, chromite occurs as irregular
pods or lenses within the host rock Major podiform
deposits are found in Kazakhstan, Albania, Greece,
Turkey, Zimbabwe, Cuba, and the Philippines
Po-diform chromites form along island arcs and mobile
mountain belts, and most are of Paleozoic age or
younger
Chromium occurs in nature only in combination
with other elements The most important chromium
ore is chromite, a brownish-black to iron-black
min-eral of the spinel group It occurs as octahedral
crys-tals, irregular masses, and alluvial deposits Other
minerals that contain chromium include the
gem-stones emerald and aquamarine, which owe their
dis-tinctive colors to the element
Chromium plays a role in the body’s glucose
toler-ance Moderate amounts of trivalent chromium in the
diet have no apparent harmful effects Chromium
metal is biologically inert and has no known toxicity
While trivalent chromium compounds exhibit
lit-tle or no toxicity, hexavalent chromium is a systemic
poison and an irritant and corrosive It can be
ab-sorbed by ingestion, inhalation, or dermal exposure
Ulcerations of the skin and mucous membranes may
result from exposure Chromate salts are suspected
human carcinogens that may produce tumors of the
lungs, nasal cavity, and paranasal sinuses The 1974
Safe Drinking Water Act set the maximum allowable
concentration for total chromium in drinking water
in the United States at 100 micrograms per liter
In general, chromium does not naturally occur in
high concentrations in water Elevated chromium
lev-els in surface water or groundwater are typical
be-cause of contamination from runoff from old mining
operations or improper disposal of electroplating
wastes However, in the groundwater of Paradise
Val-ley in Maricopa County, Arizona, hexavalent
chro-mium of natural origin is present in concentrations
exceeding 200 micrograms per liter The alkaline
groundwater causes naturally occurring trivalent mium in the soil to oxidize to soluble hexavalent chro-mium
History Chromium appears to have been unknown to ancient civilizations It was discovered in 1797 by Louis-Nicolas Vauquelin, a French chemist, when he found that the lead in a sample of crocoite (PbCrO4) from Si-beria was combined with an unknown oxide mineral Between the time of chromium’s discovery and 1827, the primary source of chromite was the Ural Moun-tains of Russia In 1827, the discovery of chromite in Maryland moved the United States to the forefront of world production Large Turkish deposits were devel-oped in the 1860’s; after this time, the Eastern Hemi-sphere became the chief source of chromite The chemical manufacturing industry was the main con-sumer of chromium until the early 1900’s, when the element found increasing use in metallurgical and re-fractory products During World Wars I and II, the United States increased its domestic production of the metal, and during the 1950’s it stockpiled domes-tic ores International polidomes-tical conflicts have often led to interruptions in chromium supply
Obtaining Chromium Sodium dichromate, from which most commercial chromium compounds are made, is produced by roasting chromite with sodium carbonate, leaching the resulting product with water, and concentrating and acidifying the leachate to cause sodium dichro-mate to precipitate Ferrochromium is prepared from chromite by reducing the ore with carbon in a blast furnace Metallic chromium is obtained by reducing chromium oxide with aluminum or carbon, or by electrolyzing a solution of ferrochromium dissolved
in sulfuric acid after the iron has been removed from the solution as ferrous ammonium sulfate Chromium metal in its purest form is produced in small quanti-ties by vapor deposition from anhydrous chromium iodide
Uses of Chromium The principal use of chromium is as an alloy metal, particularly in the steel industry Combined with other metals, it imparts hardness, strength, and resistance
to corrosion and heat Chromium facilitates the hard-ening of steel and, if the alloy’s carbon content is high, enables it to withstand extreme abrasion and
Trang 6wear In ball-bearing steel, chromium improves the
elastic limit and imparts an evenly distributed
hard-ness Chromium increases the corrosion resistance of
stainless steel and is an important alloy metal in
heat-resisting steels High-chromium steel, with its high
re-sistance to wear, is used for making items such as die
blocks, press plates, chisels, hacksaw blades, and
cir-cular steel saws Nichrome, an alloy of nickel and
chromium, is used as a heating element in household
appliances such as electric toasters and coffeepots
Stellite, an extremely hard alloy of cobalt, chromium,
and tungsten with minor amounts of iron, silicon,
and carbon, is used in metal cutting tools and
wear-resistant surfaces A similar alloy, which employs
mo-lybdenum rather than tungsten, is used in surgical
tools With its hardness and nontarnishing
proper-ties, chromium is also an ideal electroplating metal
Chromium’s uses in alloys and plating make it an
im-portant strategic and critical metal
Chromite is a valuable raw material for the
manu-facture of refractory materials such as refractory
bricks, foundry sand, and casting items for furnaces
used in metallurgy Refractory materials are able to
withstand high temperatures and contact with often
corrosive gases and molten materials Chromite is
fre-quently used in combination with other refractory
materials; for instance, mixed with the magnesium
ore magnesite (magnesium carbonate) and fused in
an arc furnace it is cast into refractory brick
Various chromates and dichromates, salts of
chro-mic acid, are used as pigments in paints and dyes,
yielding vivid yellows, reds, oranges, and greens
Chromium hydroxide is used as a mordant in textile
dyeing Potassium dichromate mixed with sulfuric
acid is used as a cleanser for laboratory glassware
Chromium compounds are also used in chemical
manufacture and leather tanning
Karen N Kähler
Further Reading
Adriano, Domy C “Chromium.” In Trace Elements in
Terrestrial Environments: Biogeochemistry,
Bioavailabil-ity, and Risks of Metals 2d ed New York: Springer,
2001
Greenwood, N N., and A Earnshaw “Chromium,
Molybdenum, and Tungsten.” In Chemistry of the
El-ements 2d ed Boston: Butterworth-Heinemann,
1997
Guertin, Jacques, et al., eds Chromium (VI) Handbook.
Boca Raton, Fla.: CRC Press, 2005
Independent Environmental Technical Evaluation
Group Chromium (VI) Handbook Edited by Jacques
Guertin, James A Jacobs, and Cynthia P Avakian Boca Raton, Fla.: CRC Press, 2005
Katz, Sidney A., and Harry Salem The Biological and Environmental Chemistry of Chromium New York:
VCH, 1994
Kogel, Jessica Elzea, et al., eds “Chromite.” In Indus-trial Minerals and Rocks: Commodities, Markets, and Uses 7th ed Littleton, Colo.: Society for Mining,
Metallurgy, and Exploration, 2006
Manning, D A C Introduction to Industrial Minerals.
New York: Chapman & Hall, 1995
Nriagu, Jerome O., and Evert Nieboer, eds Chromium
in the Natural and Human Environments New York:
Wiley, 1988
Udy, Marvin J Chemistry of Chromium and Its Com-pounds Vol 1 of Chromium New York: Reinhold,
1956
Web Sites Natural Resources Canada Canadian Minerals Yearbook, Mineral and Metal Commodity Reviews
http://www.nrcan-rncan.gc.ca/mms-smm/busi-indu/cmy-amc/com-eng.htm
U.S Geological Survey Chromium: Statistics and Information http://minerals.usgs.gov/minerals/pubs/
commodity/chromium See also: Alloys; Brazil; India; Kazakhstan; Metals and metallurgy; Plutonic rocks and mineral deposits; Rus-sia; South Africa; Steel; Strategic resources; Turkey; United States
Civilian Conservation Corps
Category: Organizations, agencies, and programs Date: Established 1933
The Civilian Conservation Corps, a central part of Franklin D Roosevelt’s “New Deal,” was conceived as
a comprehensive project which would encompass relief for the unemployed, recovery of the nation’s economic health, and conservation of American natural re-sources.
Trang 7In 1934, President Franklin D
Roose-velt noted that the United States was
one of the few industrialized countries
that had not established a “national
pol-icy for the development of our land and
water resources.” This lack was in the
process of rectification when, in March,
1933, shortly after his inauguration,
Roosevelt proposed the establishment
of the Civilian Conser vation Corps
(CCC) The legislation provided for the
voluntary mobilization of unemployed
young men to work on various
conser-vation projects throughout the nation
As Congress did on most of
Roose-velt’s proposals during his first one
hun-dred days in office, it acted swiftly,
ap-proving the legislation on March 31,
1933 Administered by the Labor
De-partment, the Army, the Forestry
Ser-vice, and the National Park SerSer-vice, the
CCC had the potential to be an administrative
disas-ter, but disaster did not happen By July more than
300,000 unemployed young men, aged eighteen to
twenty-five and from families on relief, were already
working in the CCC’s thirteen hundred camps By
1935, there were more than 500,000 men in the CCC,
and before it was dismantled more than 2.5 million
young men had joined, working for one dollar a day in
twenty-five hundred camps
Impact on Resource Use
The projects were varied, ranging from restoring
bat-tlefields of the American Revolution and Civil War to
constructing trails in the High Sierra; from protecting
wildlife (including stocking almost one billion fish)
and building fire lookout towers to planting two
bil-lion trees—200 milbil-lion as windbreaks in the Dust
Bowl Estimates indicate that of all the forests planted
in the history of the United States, both public and
private, more than half were planted by the so-called
tree people of the CCC From the east and west, north
and south, farm boys worked alongside young men
from the cities The CCC was organized on a military
basis, although participation was voluntary, and one
could enter and leave when one wished Most men
stayed from several months to about one year
Although women were excluded and African
Amer-icans were subject to a 10 percent quota and were
usu-ally segregated, as a conservation organization, the CCC was an instant and lasting success Many of Amer-ica’s natural resources were preserved during those few years of the 1930’s in spite of the predictions by some that many of the projects were beyond the gov-ernment’s powers and that the CCC would be inimical
to capitalism or to organized labor because of the CCC’s low wages Some feared that the CCC smacked
of communist collectivism or fascist militarism Not the least of the resources conserved were the young men themselves, whose experience developed their physical bodies as well as their intellectual and emo-tional capabilities At the onset of World War II the CCC was terminated, but individual states later estab-lished their own conservation corps, such as the Cali-fornia Conservation Corps John F Kennedy’s Peace Corps was also inspired in part by the CCC
Eugene Larson
Web Sites Civilian Conservation Corps Civilian Conservation Corps Legacy http://www.ccclegacy.org/
National Archives Records of the Civilian Conservation Corps http://www.archives.gov/research/guide-fed-records/groups/035.html#35.4
Members of the African American Civilian Conservation Corps reconstruct gabions
at the French Battery along York-Hampton Road in Yorktown, Virginia, in the mid-1930’s (National Park Service Historic Photograph Collection)
Trang 8See also: Conservation; Dust Bowl; Forest Service,
U.S.; Reforestation; Roosevelt, Franklin D
Clays
Category: Mineral and other nonliving resources
The term “clay” may be used to describe a group of
fine-grained minerals, a type of rock, or a range of particle
size, generally less than four micrometers As a rock
term, clay is generally understood to mean an earthy,
fine-grained material formed largely of crystalline
minerals known as the clay minerals.
Background
Clays can be found throughout the world, but
eco-nomically valuable deposits are limited in extent and
distribution Major kaolin deposits in the United States
are found in Georgia and South Carolina The
world’s major bentonite deposits are found
in Wyoming and Montana, and large fuller’s
earth deposits can be found in Georgia and
Florida Ball and refractory clays are
abun-dant in Kentucky and Tennessee
Clays are used in a number of applications
requiring the incorporation of fine-grained
materials that contribute to a product’s
physi-cal or chemiphysi-cal properties Uses include fillers
in paint, paper, and plastics, additives to
drill-ing muds, the manufacture of ceramics and
brick, carriers for pesticides and insecticides,
the manufacture of catalysts, and cosmetic
and pharmaceutical uses
Clays are considered “industrial minerals,”
a group of minerals composed of geological
materials having commercial value and of a
nonmetallic, nonfuel character They may be
marketed in a natural, as-mined state or as
processed materials Clays can vary widely in
composition and physical characteristics
Cer-tain similarities exist among a number of clays,
however, and they can be categorized in broad
terms as kaolin, bentonite or fuller’s earth,
ball clay, and refractory clay based on
similari-ties in either composition or functional
per-formance Clays that do not fall into any of the
major categories are generally referred to as
common clay or shale
Mineralogy and Chemistry Clays are hydrous (water-containing) aluminum sili-cates containing alkalies or alkaline earth elements Magnesium or iron may substitute wholly or partially for aluminum in the clay mineral structure Clay min-erals are composed of alternating layers of two differ-ent atomic structures The first is an aluminum-bear-ing octahedral sheet structure, and the second is a layer of silica tetrahedrons The aluminum and sili-con atoms are chemically bonded to oxygen in these layers, which are held to one another by weaker elec-trostatic bonds Interlayer sites in many clays contain water molecules or cations such as calcium, sodium, potassium, magnesium, lithium, or hydrogen The presence or absence of interlayer molecules affects both the physical and chemical properties of the clay
Kaolin Kaolin is a clay consisting predominantly of pure kaolinite or related clay minerals Most major
Bricks and concrete block 65%
Structural concrete 3.5%
Portland &
other cements 19%
Ceramics, glass, & tile 3%
Other 9.5%
Source:
Historical Statistics for Mineral and Material Commodities in the United States
Note:
U.S Geological Survey, 2005, clay and shale statistics, in T D Kelly and G R Matos, comps.,
, U.S Geological Survey Data Series 140 Available online at http://pubs.usgs.gov/ds/ 2005/140/.
“Other” includes ceramics and glass, floor and wall tile, highway surfacing, other lightweight aggregates, refractories, and other heavy clay products.
U.S End Uses of Clay and Shale
Trang 9its of kaolin are referred to as either primary
(resid-ual) or secondary Primary deposits are formed in
place as the weathering products of granite or other
feldspar-rich rocks Other minerals associated with
deposits of this type include quartz, micas,
amphi-boles, tourmaline, and unweathered feldspars
Pri-mary deposits are irregular in shape, grading
down-ward into unaltered parent (source) rock
Secondary deposits of kaolin are sedimentary
ac-cumulations of kaolinitic material that has been
trans-ported from its source area Deposits of this type may
contain up to 95 percent kaolinite; in contrast,
pri-mary deposits may contain as little as 10 percent
Asso-ciated minerals may include quartz, micas, other clay
minerals, and a variety of high-density “heavy
miner-als.” Secondary deposits are generally lenticular or
tabular in shape, with thicknesses up to sixty meters
and areal dimensions of up to about two kilometers
Kaolin is also found as a product of hydrothermally
altered rocks Deposits of this nature are of limited
size and extent They occur as irregularly elongated
pods or pipelike bodies along faults, joints, and other
conduits along which hot solutions have flowed
Kaolin is generally soft and plastic, although harder
silica-bearing varieties also exist Crystals of kaolinite
are hexagonal, composed of individual platelets
stacked in an accordion-like manner There is little ionic substitution in the crystal lattice
Kaolin has numerous industrial uses and is perhaps best known for its use in the manufacture of china and porcelain Its chemical inertness, high brightness, white color (either naturally or resulting from pro-cessing and beneficiation), and crystal shape make it useful in other applications as well Kaolin is used as a filler or coating in the manufacture of paper, as a filler
in paint, plastics, and pharmaceuticals, and in the manufacture of rubber, tile, brick, ink, adhesives, de-tergents, cosmetics, pencils, pastes, and other con-sumer products
Ball Clay and Refractory Clay Ball clays are composed of up to 70 percent kaolin They generally occur in secondary sedimentary de-posits characterized by the presence of organic matter along with varying amounts of other clays, quartz, feldspar, calcite, and heavy minerals Sedimentary de-posits of ball clay represent accumulations of clay ma-terials that were derived from a number of sources and that were deposited in nonmarine environments Most deposits are lenticular, with areal dimensions of
up to 850 meters and thicknesses of up to 10 or more meters
Clay and Shale: World Mine Production, 2008
Metric Tons
Commonwealth of Independent
Source: Data from the U.S Geological Survey, Mineral Commodity Summaries, 2009 U.S Government Printing Office, 2009.
Trang 10Ball clays are plastic or semi-plastic and are used to
provide strength and malleability to ceramic bodies
prior to firing They fuse during firing, also acting as a
“cement” to bind together the refractory,
nonshrink-ing component of a ceramic body Ball clay is used to
manufacture tableware, stoneware, tiles, plumbing
fixtures, and bricks It is also used as a sealant in
land-fills
Refractory clays are generally kaolin, containing
only small quantities of mica or iron-bearing minerals
that might combine with other materials during firing
to form low-melting-point glasses Refractory clays
have a high heat resistance Other properties that
af-fect overall quality include shrinkage, warping,
crack-ing, and abrasion Refractory clays can be soft and
plastic or hard like flint They generally occur as
sedi-mentary deposits that are lenticular or tabular in
shape They are mined for use in the manufacture of
firebrick, insulating brick, and other heat-resistant
clay products
Bentonite and Fuller’s Earth
“Bentonite” is generally understood to mean a clay
consisting of minerals from the montmorillonite
group, regardless of origin or occurrence The most
important commercial montmorillonites are the
so-dium and calcium varieties Soso-dium montmorillonite
(Wyoming or western bentonite) has high swelling
ca-pabilities when added to water Calcium
montmorillo-nite (southern bentomontmorillo-nite) has a lower swelling
capac-ity, and it generally crumbles when added to water
Other montmorillonites include those rich in lithium
(hectorite), magnesium (saponite), or iron
(non-tronite)
Bentonite can be both physically and chemically
reactive It shrinks or swells as it releases or absorbs
interstitial water or organic molecules, and it has
important cation exchange and chemical sorption
properties Bentonite’s physical and chemical
prop-erties account for its usefulness in modifying fluid
viscosity or plasticity; it also has a variety of other
uses Bentonites can be modified through chemical
treatment to enhance selected physical or chemical
properties
Wyoming bentonites are suitable for use in an
as-mined condition They are used as an additive in
drill-ing mud to increase viscosity and aid in the removal of
drillhole cuttings The clay also helps maintain
cut-tings in suspension and creates an impervious coating
on the wall of the drillhole to prevent fluid loss during
drilling Southern bentonites can be modified to have properties similar to Wyoming bentonites, but their use is generally restricted to other applications such as binding iron ore during pelletizing and the manufac-ture of catalysts and no-carbon-required (NCR) copy papers Bentonites are also used to refine, decolor, and purify oils and beverages; to manufacture fire re-tardants; and as hydraulic barriers
“Fuller’s earth” refers to clays (generally benton-itic) suitable for bleaching and absorbent or other special uses The term was first used to describe mate-rials used for cleansing or fulling wool (removing lanolin and dirt), but it is now used more broadly to include decolorizers or purifiers in filtering applica-tions Fuller’s earth products include cat litter, pesti-cide and insectipesti-cide carriers, soil conditioners, light-weight aggregate, and pharmaceuticals
Mining and Processing Most clay deposits are mined from open pits, al-though some are mined by underground methods Open-pit mining generally involves the stripping of overburden, excavation of the clay, and transport of mined material to the processing plant Some opera-tions may require blasting
The simplest operations involve excavation, trans-port to the plant, drying, and shipment to the cus-tomer More complex operations may require that the mined material first be put into a slurry form for re-moval of grit or sand, with transport to the plant by pipeline Clay slurries can be chemically or physically treated to remove contaminants that contribute to discoloration or poor chemical or physical perfor-mance They can then be filtered and dried prior to packaging and shipment to the customer Some clays are put back into slurry form prior to shipment, de-pending upon a customer’s needs
Kyle L Kayler
Further Reading Bergaya, Fạza, Benny K G Theng, and Gerhard
Lagaly, eds Handbook of Clay Science New York:
Elsevier, 2006
Chatterjee, Kaulir Kisor “Clay.” In Uses of Industrial Minerals, Rocks, and Freshwater New York: Nova
Sci-ence, 2009
Kogel, Jessica Elzea, et al., eds “Clays.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses.
7th ed Littleton, Colo.: Society for Mining, Metal-lurgy, and Exploration, 2006