Lead Category: Mineral and other nonliving resources Where Found Lead is widely distributed in the Earth’s crust; it has an estimated percentage of the crustal weight of 0.0013, making i
Trang 1Further Reading
Atlas, Ronald M., and Richard Bartha Microbial
Ecol-ogy: Fundamentals and Applications 4th ed Menlo
Park, Calif.: Benjamin/Cummings, 1998
Burkin, A R “Chemistry of Leaching Processes.” In
Chemical Hydrometallurgy: Theory and Principles
Lon-don: ICP, 2001
Keller, Edward A Environmental Geology 8th ed Upper
Saddle River, N.J.: Prentice Hall, 2000
Killham, Ken Soil Ecology New York: Cambridge
Uni-versity Press, 1994
Madigan, Michael T., John M Martinko, Paul V
Dunlap, and David P Clark Brock Biology of
Microor-ganisms San Francisco: Pearson/Benjamin
Cum-mings, 2009
Marsden, John, and C Iain House “Leaching.” In The
Chemistry of Gold Extraction 2d ed Littleton, Colo.:
Society for Mining, Metallurgy, and Exploration,
2006
Robertson, G P., and P M Groffman “Nitrogen
Transformations.” In Soil Microbiology, Ecology, and
Biochemistry, edited by Eldor A Paul 3d ed Boston:
Academic Press, 2007
See also: Biotechnology; Igneous processes, rocks,
and mineral deposits; Mining wastes and mine
recla-mation; Secondary enrichment of mineral deposits;
Sedimentary processes, rocks, and mineral deposits;
Soil degradation
Lead
Category: Mineral and other nonliving resources
Where Found
Lead is widely distributed in the Earth’s crust; it has an
estimated percentage of the crustal weight of 0.0013,
making it more common than silver or gold but less
common then copper or zinc; these are the four
min-erals with which lead is most commonly found in ore
deposits All five may occur together in a deposit, or
only two or three may occur in concentrations
suffi-ciently rich to be economically attractive to miners
Primary Uses
The major use of lead in the United States is in the
lead-acid batteries used in automotive vehicles
Be-cause lead is so toxic, a fact that has been known since
ancient times, many of its former uses have been cur-tailed or discontinued While it is still used in cables, ammunition, solders, shielding of radiation, and elec-trical parts, its use as an antiknock additive in gasoline was phased out during the 1970’s and 1980’s Never-theless, lead production has been maintained at about the same level as before the phase out Should a suit-able substitute ever be developed for lead-acid batter-ies, the use of lead will decline to very low levels Technical Definition
Lead (abbreviated Pb), atomic number 82, belongs to Group IV of the periodic table of the elements It is a mixture of four stable isotopes and has twenty-seven other isotopes, all radioactive, resulting from the fact that lead is the end product of three series of radioac-tive elements: the uranium series, actinium series, and thorium series It has an average atomic weight of 207.2 and a density of 11.35 grams per cubic centime-ter; it has a melting point of 327.5° Celsius and a boil-ing point of 1,740° Celsius
Description, Distribution, and Forms Lead is soft, malleable, and ductile, and is second only
to tin in possessing the lowest melting point among the common metals It may well have been the first metal smelted by humans, although it was probably not the first metal used—an honor claimed by gold, silver, or copper, which occur naturally in their metal-lic states The fact that the principal ore of lead, galena (lead sulfide), frequently resembles the metal itself in its gray-black metallic color probably encour-aged early humans to experiment with crude smelt-ing Inorganic lead also occurs as a carbonate (cer-rusite), sulfate (anglesite), and oxides Organic compounds of lead exist; these were used for many years in automobile gasoline as antiknock additives (tetraethyl and tetramethyl lead) Lead is widely dis-tributed in the environment, but except in bedrock, concentrations are largely a consequence of human activity Clair Patterson demonstrated that dramatic human-related increases in lead concentrations exist
in the oceans, in polar ice sheets, and in the atmo-sphere Before the human use of lead, the global flux into the oceans was only one-tenth to one-hundredth what it is today; lead in the atmosphere has increased
a hundredfold globally and a thousandfold in urban areas
Considering that only an estimated 0.0013 percent
of the Earth’s crust is lead, it is surprisingly widely
Trang 2dis-tributed in the environment Lead is found in both
crystalline (igneous and metamorphic) and
sedimen-tary rocks Because it is the stable end product of
ra-dioactive disintegration of minerals that form in
igne-ous rocks (it is the rate of this disintegration that is
employed to determine the age of the rock), virtually
all older crystalline rocks contain at least tiny amounts
of lead As sedimentary rocks are derived from the
weathering, erosion, and sedimentation of fragments
from existing rocks, it follows that lead compounds
will be among those that are sedimented The higher
concentrations of lead—those that pose toxicity prob-lems or are valuable to miners—depend upon quite different processes Some toxic concentrations of lead are transported by water and then sedimented or ab-sorbed by rock particles, depending on the salinity or acidity levels of the solution Most toxic concentra-tions of lead, however, are transported as dust by the atmosphere
Deposits of lead ore exist at far higher concentra-tions than those levels that pose problems in water, dust, or soil They are the result of natural geologic
Data from the U.S Geological Survey, U.S Government Printing Office, 2009.
47,000 145,000 35,000
335,000
53,000 48,000 69,000
440,000 300,000
Metric Tons of Lead Content
1,750,000 1,500,000
1,250,000 1,000,000
750,000 500,000
250,000 United States
Poland
Peru
Morocco
Mexico
Kazakhstan
South Africa
Sweden
Other countries
576,000
95,000
1,540,000
85,000 56,000
Ireland
India
China
Canada
Australia
Lead: World Mine Production, 2008
Trang 3processes, including igneous intrusions, mountain
building, and the flow of hot and cold solutions
through bedrock over millions of years The richest
lead ores may contain 20 to 25 percent lead, usually
with substantial fractions of zinc and minor quantities
of silver Copper and gold are also frequently
associ-ated with lead deposits, or vice versa (minor amounts
of lead are usually found in copper ore)
Lead affects the environment in two major ways:
through mining and processing, and because many
of its uses, particularly in the past, have exposed the
general public to its toxicity Lead mining has
envi-ronmental impacts similar to those of the mining of
any mineral Surface mining destroys the local
eco-system and disrupts the use of land for other
pur-poses; reclamation rarely prepares the land for as
valuable a use as it enjoyed before mining The
major-ity of lead is mined underground, where surface
dis-ruption is not as great unless subsidence over the
mined areas is a problem In both surface and
un-derground mining, water is generally contaminated,
mine wastes must be stored (waste dumps frequently
occupy more space than the mine itself), and the
transportation of mine products and waste serves as a
source of dust, noise, and disruption to the
surround-ing population The millsurround-ing, smeltsurround-ing, and refinsurround-ing of
lead pose further problems First, lead itself escapes
and pollutes the atmosphere with toxic substances
Second, most lead is derived from sulfides, which
upon heating in the smelting and refining processes
form sulfur dioxide Sulfur dioxide combines with
water in the atmosphere to create sulfuric acid, which
devastates and denudes the vegetation cover in the
immediate vicinity and contributes to acid rain fallout
generally
Humans may come into contact with lead and its
toxic effects in the air, dust, and water, and by direct
contamination of food, drink, or cosmetics The effects
of lead on human health are diverse and severe, with
their greatest impact on children The effects are
exac-erbated by the fact that lead accumulates in the body,
and damage is often irreversible—especially damage
to the brain Lead damages blood biochemistry, the
renal and endocrine system, liver functions, and the
central nervous system, and it contributes to
osteopo-rosis, high blood pressure, and reproductive
abnor-malities The Environmental Protection Agency and
the Occupational Safety and Health Administration
set standards of acceptable levels of lead in air, dust,
soil, and water; the standards are updated frequently
based on new research, and they are quite complex, depending on the duration and nature of exposure History
While lead apparently was not the first or second metal to attract early humans, because it did not occur
in a metallic state, it was exploited relatively early and may have been smelted in Anatolia (modern day Tur-key) as early as 7000-6500 b.c.e The softness and mal-leability of lead proved to be both attractive and unde-sirable to people in antiquity Most early lead mining was carried on to recover the associated silver, and the lead remaining from the process was piled in waste heaps Lead may be strengthened by alloying with other metals, but this process was carried out only to a limited degree in lead’s earliest usage
While lead may not have proved attractive for uses requiring strength and hardness, its malleability caused the Romans, in particular, to put it to wide-spread use in piping, roofing, and vessels In addition, lead compounds were used in paints, cosmetics, and
as additives to wine and food Lead poisoning was therefore widespread The problem was recognized possibly as early as 370 b.c.e by Hippocrates and cer-tainly was known by Nikander in the second century b.c.e The Romans nevertheless continued to press lead into a variety of services until the fall of their em-pire Some authorities believe that lead poisoning was central to this fall, and many more believe that it at least contributed (especially to the disorganization of Roman leaders) Others maintain that the critical lead-related factor in the decline of Rome was the ex-haustion of the richer silver-bearing ores Exex-haustion
of mines or ores at any period in history is usually a function of the technology and economics of the time; many of these ores were particularly rich by modern standards Silver was critical to maintenance
of the Roman financial system, and the decline in its availability brought economic chaos
Medieval production of lead declined dramatically
in Europe following the fall of the Roman Empire, al-though recurring cases of lead poisoning during this period serve as a reminder that lead was still utilized widely in storage vessels The Industrial Revolution, beginning with its earliest stages, revived the produc-tion level of lead, both for itself and as a by-product of silver mining The expansion of European explora-tion into the Western Hemisphere and of European colonization worldwide from the fifteenth century onward undoubtedly contributed to the rise in lead
Trang 4production Gold and silver were sought avidly in
these expansions of domain, and lead mining
fre-quently serves as the final use or “mop-up” stage in the
life history of a mining district Also, industrial uses
and mining technology became increasingly
sophisti-cated, leading to a new demand for lead and zinc, its
frequent associate, especially beginning in the
nine-teenth century The production curve of lead and
zinc goes exponentially upward through history, with
far greater production today than in earlier centuries
Obtaining Lead
The largest lead deposits in the United States and
Eu-rope are of the Mississippi Valley type: lead sulfide
(ga-lena) deposits of uncertain origin in limestone or
do-lomite rocks Many large mines throughout the world
are found in crystalline rocks, where they are usually
associated with igneous intrusions Some lead is
re-covered as a by-product of the mining of copper or
other associated minerals from large open-pit mines
developed in low-grade ores, called porphyries This
type of recovery is a triumph of modern technology
and engineering, because the ores frequently contain
less than 0.5 percent copper, with even smaller
frac-tions of lead Most lead is recovered from
under-ground mines that are exploiting much smaller
con-centrations in veins or disseminated beds of lead-zinc,
zinc-lead, or lead-silver ores
From 2003 to 2007, the average U.S primary lead
production (lead from mines) was 162,000 metric tons
per year, while production of secondary lead (recycled
from scrap, chiefly automotive
bat-teries) during the same time period
was 1.2 million metric tons per year
World mine production was
some-what less than lead from secondary
sources: about 3.5 million metric
tons from mines compared to 3.8
million metric tons from secondary
sources Recycling should prove
even more important in the future
as the richest deposits—those in
which the lead content of the ore
ranges between 5 and 10 percent—
are depleted This type of
“exhaus-tion” of a deposit is a function of
the prevailing technology and
eco-nomics In the first half of the
twen-tieth century, the tristate lead-zinc
mining district of Missouri,
Okla-homa, and Kansas was the world’s greatest Produc-tion there essentially ceased in the 1950’s, not because the lead and zinc were literally exhausted but because the concentrations available dropped below the level
at which mining could be done profitably
Technology is continuously improving, however, and the history of mining is filled with examples (par-ticularly concerning the five associated metals gold, silver, copper, lead, and zinc) in which improvements
in technology, combined with changing economic conditions, have made it possible to reopen or rework older and less attractive deposits Some mine tailings
or waste dumps have been reworked several times un-der these circumstances
Uses of Lead More than most metals, the uses to which lead and lead compounds have been put have changed consid-erably throughout history One reason is that new op-portunities have presented themselves, such as auto-motive lead-acid batteries, the shielding of dangerous radiation, and antiknock additives for gasoline—all twentieth century phenomena Largely, however, this has occurred because people have become increas-ingly cognizant of the dangers posed by lead’s toxicity While the dangers of exposure to lead have been known since Greek and Roman times, in few cases has this led to regulation of uses Not until the 1960’s, 1970’s, and 1980’s were specific controls or regula-tions imposed restricting the use of lead in paint pig-ments, as an additive to gasoline, and in construction
U.S End Uses of Lead
Percentage Uses
88 Lead-acid batteries
10 Ammunition, casting material, pipes, radiation
shields, traps, extruded products, building construction, cable covers, caulking, solder, oxides (for ceramics, chemicals, glass, pigments)
2 Ballast, counterweights, brass, bronze, foil,
terne metal, type metal, wire, other
Source: Data from the U.S Geological Survey, Mineral Commodity Summaries, 2009.
U.S Government Printing Office, 2009.
Trang 5Lead piping is still found in structures built in the
1970’s; the use of lead in storage vessels for food or
drink has been regulated even more recently Lead
foil was used in capping wine bottles into the early
1990’s, and many people are still unaware that storage
of wine or other liquids in fine leaded-glass decanters
permits leaching of the lead content into the fluid
over time
The post-World War II era saw the elimination or
substantial reduction of the following uses of lead:
water pipes, solder in food cans, paint pigments,
gaso-line additives, and fishing sinkers The major
remain-ing uses include storage batteries, ammunition, paint
pigments (for nonresidential use), glass and
ceram-ics, sheet lead (largely for shielding against
radia-tion), cable coverings, and solder
Neil E Salisbury
Further Reading
Adriano, Domy C “Lead.” In Trace Elements in
Terres-trial Environments: Biogeochemistry, Bioavailability, and
Risks of Metals 2d ed New York: Springer, 2001.
Casas, José S., and José Sordo, eds Lead: Chemistry,
An-alytical Aspects, Environmental Impact, and Health
Ef-fects Boston: Elsevier, 2006.
Cheremisinoff, Paul N., and Nicholas P
Cherem-isinoff Lead: A Guidebook to Hazard Detection,
Re-mediation, and Control Englewood Cliffs, N.J.: PTR
Prentice Hall, 1993
English, Peter C Old Paint: A Medical History of
Child-hood Lead-Paint Poisoning in the United States to 1980.
New Brunswick, N.J.: Rutgers University Press,
2001
Greenwood, N N., and A Earnshaw “Germanium,
Tin, and Lead.” In Chemistry of the Elements 2d ed.
Boston: Butterworth-Heinemann, 1997
Guilbert, John M., and Charles F Park, Jr The Geology
of Ore Deposits Long Grove, Ill.: Waveland Press,
2007
Massey, A G “Group 14: Carbon, Silicon,
Germa-nium, Tin, and Lead.” In Main Group Chemistry 2d
ed New York: Wiley, 2000
National Research Council Lead in the Human
Envi-ronment: A Report Washington, D.C.: National
Academy of Sciences, 1980
Nriagu, Jerome O Lead and Lead Poisoning in
Antiq-uity New York: Wiley, 1983.
Warren, Christian Brush with Death: A Social History of
Lead Poisoning Baltimore: Johns Hopkins
Univer-sity Press, 2000
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 Lead: Statistics and Information http://minerals.usgs.gov/minerals/pubs/
commodity/lead See also: Air pollution and air pollution control; Metals and metallurgy; Mineral resource use, early history of; Recycling; Silver; United States; Zinc
Leopold, Aldo
Category: People Born: January 11, 1887; Burlington, Iowa Died: April 21, 1948; near Baraboo, Sauk County, Wisconsin
In his years of government service and private work, Leopold was active in game management and wildlife preservation His Sand County Almanac was influ-ential with succeeding generations of conservationists.
Biographical Background Aldo Leopold, born in Burlington, Iowa, graduated from the Yale Forest School (now the Yale School of Forestry and Environmental Studies) in 1906 In 1909, after completing his master’s degree, he joined the U.S Forest Service and fostered the ecological poli-cies of Gifford Pinchot and Theodore Roosevelt Sta-tioned in the southwestern United States, he advo-cated game conservation to avoid the erosion of sport hunting He also helped establish a 200,000-hectare roadless wilderness in the Gila National Forest While pursuing wolf eradication to ensure deer viability, he realized the importance of ecological interactions
Impact on Resource Use Leopold moved to Wisconsin in 1924, joined the U.S Forest Products Laboratory, and developed the policy
of wildlife management He published Game Manage-ment, subsequently retitled Wildlife ManageManage-ment, in
1933 In the same year, he joined the University of
Trang 6Wis-consin at Madison Department of Agricultural
Eco-nomics He assisted Robert Marshall in creating the
Wilderness Society in 1935, and he established a
one-man Department of Wildlife Management in 1939
Leopold advocated integration of local concerns
with universities, government agencies, and the
pri-vate sector to balance farming, forestry, wildlife, and
recreation He escaped on the weekends to his sand
farm in Wisconsin, where he wrote prolifically His
Sand County Almanac, published posthumously in
1949, represents a lifetime of observations
concern-ing ecology, ethics, and aesthetics and concludes that
a policy is right when it tends to preserve the integrity,
stability, and beauty of the biotic community; any
other policy, according to Leopold, is wrong
Aaron S Pollak and Oliver B Pollak
See also: Conservation; Pinchot, Gifford; Roosevelt,
Theodore; Wilderness; Wilderness Society
Lime
Category: Mineral and other nonliving resources
Where Found Lime is a manufactured product not found in nature
It is usually derived from the common sedimentary rocks limestone, dolomitic limestone, and dolostone, although it can also be produced from other high-calcium materials such as marble, aragonite, chalk, shell, and coral
Primary Uses
An essential industrial chemical, lime is used in the manufacture of steel, pulp and paper, glass and porce-lain, and chemicals It is a component of construction materials such as plaster, mortar, stucco, and white-wash It is also used in conditioning acidic soils, soft-ening water, and treating wastewater and smokestack emissions
Technical Definition Lime (also known as quicklime, caustic lime, or calcia) is a common term for the chemical compound calcium oxide (CaO) The name is often applied to several related compounds, including hydrated or slaked lime (calcium hydroxide, Ca(OH)2); dolomitic quicklime (CaOCMgO); type N (Ca(OH)2CMgO) and type S (Ca(OH)2CMg(OH)2) dolomitic hydrates; and refractory lime, also called dead-burned or hard-burned lime When pure, lime occurs as colorless, cu-bic crystals or in a white microcrystalline form; often impurities such as iron and oxides of silicon, alumi-num, and magnesium are present Lime has a specific gravity of 3.34, a melting point of 2,570° Celsius, and a boiling point of 2,850° Celsius
Description, Distribution, and Forms
A highly reactive compound, lime combines with water to produce the more stable hydrated lime This reaction, known as slaking, produces heat and causes the solid almost to double in volume At temperatures around 1,650° Celsius, lime recrystallizes into the coarser, denser, and less reactive refractory lime When heated to approximately 2,500° Celsius, lime is incan-descent
Lime is a highly reactive manufactured compound that is an essential part of many industrial processes
An alkali, it dissolves in water to produce a caustic,
Aldo Leopold’s seminal Sand County Almanac (1949) has
influ-enced generations of conservationists (AP/Wide World Photos)
Trang 7sic solution Lime is typically obtained from
lime-stone, although other natural substances that are
high in calcium are also used as raw materials for lime
manufacture Total world production of lime
ap-proaches 300 million metric tons, about 20 million
metric tons of which are produced in the United
States (including Puerto Rico) From 2003 to 2007,
the United States was second to China in lime
produc-tion
History
Use of lime in construction dates back at least to the
ancient Egyptians, who, between 4000 and 2000 b.c.e.,
employed it as a mortar and plaster The Greeks,
Ro-mans, and Chinese used it in construction,
agricul-ture, textile bleaching, and hide tanning One of the
oldest industries in the United States, lime
manufac-ture began in colonial times While the use of lime
in-creased with the Industrial Revolution, it remained
largely a construction material until the early
twenti-eth century, when it became a crucial resource for the
rapidly growing chemical industry
Obtaining Lime
Lime may be prepared from a variety of naturally
oc-curring materials with a high calcium content While
lime is commonly obtained from limestone, a
sedi-mentary rock composed chiefly of calcite (calcium
carbonate, CaCO3), it can also be derived from
dolo-stone, a similar sedimentary rock that is
predomi-nantly dolomite (CaMg(CO3)2), or from rock with
an intermediate composition (dolomitic limestone)
Lime is also produced from marble, aragonite, chalk,
shell, and coral (all mostly calcium carbonate)
Be-cause the raw materials for lime manufacture are
plentiful and widespread, lime is produced all over
the world, with production facilities generally located
near the sources for the raw materials
When calcium carbonate is heated in a masonry
furnace to about 1,100° Celsius, it breaks down into
lime and carbon dioxide Heating dolomite in this
fashion produces dolomitic quicklime and carbon
di-oxide Approximately 100 metric tons of pure
lime-stone yields 56 metric tons of lime Adding water to
stabilize lime or dolomitic quicklime yields the
hy-drated (slaked) form Dolomite is typically used to
make refractory (dead-burned) lime, which involves
heating the materials to temperatures around 1,650°
Celsius
Uses of Lime
A fundamental industrial chemical, lime is used in the manufacture of porcelain and glass, pigments, pulp and paper, varnish, and baking powder It is em-ployed in the preparation of calcium carbide, calcium cyanamide, calcium carbonate, and other chemicals;
in the refining of salt and the purification of sugar; in treating industrial wastewater, sewage, and smoke-stack effluent; and in softening water In metallurgy it
is used in smelting and in concentrating ores Lime and other calcium compounds are used in liming, a method for treating acidic soils The application of lime to soil neutralizes acidity, improves soil texture and stability, and enriches the soil’s nitrogen content
by increasing the activity of soil microorganisms that secure nitrogen from the air Lime’s incandescing properties are employed in the Drummond Light, or limelight, in which a cylinder of lime is heated with the flame of an oxyhydrogen torch to produce a bril-liant white light Mixed with sand and water, lime serves as a mortar or plaster The lime hydrates in
Chemical &
industrial 23%
Metallurgical 36%
Construction 13%
Environmental 28%
Source:
Historical Statistics for Mineral and Material Commodities in the United States
Note:
U.S Geological Survey, 2005, lime 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/.
Miscellaneous “other” uses of 1% are included in the categories above.
U.S End Uses of Lime
Trang 8combination with water; the mortar hardens quickly
as the hydrated lime reacts with carbon dioxide in the
air to form calcium carbonate Dolomitic quicklime is
used to produce a hard, strong, and elastic stucco
Uses of hydrated lime include soil liming, sugar
re-fining, and chemical preparation In leather tanning,
hydrated lime is used to remove hair from hides In
construction, it is used to increase the durability of
mortar, plaster, and stucco Hydrated lime in a highly
dilute solution is whitewash Filtering whitewash yields
lime water, used in medicine as a burn treatment
and as an antacid, and in chemistry as a reagent
Dolomitic hydrates are used as a flux in the
manufac-ture of glass
Dead-burned lime is a refractory material, able to
withstand contact with often corrosive substances at
elevated temperatures Refractory lime is a
compo-nent in tar-bonded refractory brick, which is used in
the construction of the basic oxygen furnaces
em-ployed in steelmaking
Karen N Kähler
Further Reading
Boggs, Sam “Limestones.” In Petrology of Sedimentary
Rocks 2d ed Cambridge, England: Cambridge
University Press, 2009
Boynton, Robert S Chemistry and Technology of Lime
and Limestone 2d ed New York: Wiley, 1980.
Jensen, Mead L., and Alan M Bateman Economic
Min-eral Deposits 3d ed New York: Wiley, 1979.
Kogel, Jessica Elzea, et al., eds “Lime.” In Industrial
Minerals and Rocks: Commodities, Markets, and Uses.
7th ed Littleton, Colo.: Society for Mining,
Metal-lurgy, and Exploration, 2006
Oates, J A H Lime and Limestone: Chemistry and
Tech-nology, Production and Uses New York: Wiley-VCH,
1998
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
Lime: Statistics and Information
http://minerals.usgs.gov/minerals/pubs/
commodity/lime
See also: Calcium compounds; China; Glass; Lime-stone; Metals and metallurgy; Oxides
Limestone
Category: Mineral and other nonliving resources
Limestone is one of the most widely used rock materials.
It is used as road metal, as aggregate for macadam and concrete, and as a building stone.
Definition Limestone is a widespread marine sedimentary rock found wherever shallow seas once encroached onto continents Limestone accounts for 10 to 15 percent
of all sedimentary rocks Some limestones are formed
in lakes, around springs, at geysers, and in caves The term “limestone” encompasses many rocks of diverse appearance that have calcite as their essential compo-nent They differ considerably in texture, color, struc-ture, and origin
Overview Although limestones may form by inorganic precipi-tation of calcite in lakes, springs, or caves, the most widespread limestones are of marine origin Most limestones are formed by organic processes and con-sist largely of the shells and shell fragments of marine invertebrates Because calcite is susceptible to solu-tion and recrystallizasolu-tion, diagenetic processes may completely alter the texture of the original rock Limestone is a sedimentary rock composed largely
of the mineral calcite (calcium carbonate) This rela-tively soft stone in its pure form is white, but it may be buff, pink, red, gray, or black, depending upon minor materials present The texture ranges from fine- to coarse-grained and from highly porous to highly com-pact Many limestones contain abundant fossils Dolo-stone is a closely related rock composed primarily of dolomite (calcium-magnesium carbonate)
Coquina is a limestone of comparatively recent formation consisting of loosely cemented shell frag-ments Compact rocks with abundant shell material are known as fossiliferous limestone They may be de-scribed more specifically by adding the dominant fos-sil genera to the rock name Chalk is a fine-grained, porous, white rock made up of minute tests of fo-raminifera Lithographic limestone is a compact,
Trang 9grained rock that is used in the printing process from
which it derives its name Travertine is an inorganic
deposit usually formed in caves as coarse, crystalline
dripstone Tufa is a porous, spongy material
depos-ited around springs and geysers Oolitic limestone is
composed of small, spherical bodies of concentrically
layered calcite formed in shallow water with moderate
agitation Coarse crystalline limestone forms by
re-crystallization of primary, fine-grained limestones
Limestone and other soluble rocks in warm, humid
regions are susceptible to solution by meteoric water
at the surface and in the subsurface The resulting
landscapes, characterized by abundant sinkholes and
caverns, are known as karst topography Because water
moves rapidly into the subsurface in karst regions,
rapid spreading of contamination in groundwater is
of special concern
Some limestones that take a good polish are
mar-keted as marble Limestone is used as a flux in
open-hearth iron smelters It is a basic raw material in the
manufacture of portland cement It is also used as
an inert ingredient in pharmaceutical preparations Limestone is the chief source of chemical and agricul-tural lime It is also ground and pressed to make black-board chalk Limestone serves as a significant aquifer, and it constitutes about 50 percent of reservoir rocks for oil and gas Prior to the introduction of electric lighting, carved chunks of limestone were fed into a gas flame to produce a fairly bright light used as stage lighting—hence the term “limelight.”
René A De Hon
Further Reading
Boggs, Sam “Limestones.” In Petrology of Sedimentary Rocks 2d ed Cambridge, England: Cambridge
University Press, 2009
Boynton, Robert S Chemistry and Technology of Lime and Limestone 2d ed New York: Wiley, 1980 Kogel, Jessica Elzea, et al., eds “Lime.” In Industrial Minerals and Rocks: Commodities, Markets, and Uses.
Lower magnesian limestone in Dane County, Wisconsin (USGS)
Trang 107th ed Littleton, Colo.: Society for Mining,
Metal-lurgy, and Exploration, 2006
Oates, J A H Lime and Limestone: Chemistry and
Tech-nology, Production and Uses New York: Wiley-VCH,
1998
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
Lime: Statistics and Information
http://minerals.usgs.gov/minerals/pubs/
commodity/lime
See also: Aggregates; Carbonate minerals; Cement
and concrete; Groundwater; Marble; Oil and natural
gas reservoirs; Quarrying
Lithium
Category: Mineral and other
nonliving resources
Where Found
Lithium makes up about 0.006 percent
of the Earth’s crust and is found as a
trace element in most rocks The most
important lithium ore is spodumene,
with extensive deposits in North
Caro-lina, Canada (Quebec), Brazil,
Argen-tina, Spain, and the Democratic
Repub-lic of the Congo Another important
commercial source of lithium is
lepido-lite
Primary Uses
In combination with other metals,
lith-ium is used as a heat exchanger in
nu-clear reactors as well as a radiation
shield around reactors Lithium is used
as an anode in high-voltage batteries,
and lithium compounds are used in the
manufacture of rubber products,
ce-ramic products, enamels, dyes, glass,
and high-temperature lubricants
Technical Definition Lithium, symbol Li, is located in Group IA of the peri-odic table It has an atomic number of 3 and an atomic weight of 6.941 It is a soft, silvery-white metal and is the lightest known metal It has a melting point of 180.54° Celsius, a boiling point of 1,347° Celsius, a specific gravity of 0.534, and a specific heat of 0.79 cal-orie per gram per degree Celsius
Description, Distribution, and Forms Lithium quickly becomes covered with a gray oxida-tion layer when it is exposed to air, and because it com-bines so easily with other elements, lithium is always found chemically bonded in nature Although a highly reactive element, lithium is less reactive than the other alkali metals Like the other alkali metals, it easily gives
up an electron to form monovalent positive ions History
Lithium was discovered by Swedish industrialist Johan August Arfwedson in 1817 The element was first iso-lated in 1818 by Sir Humphry Davy through electro-lytic reduction of the lithium ion
Batteries 25%
Ceramics
& glass 18%
Lubricating greases 12%
Pharmaceuticals
& polymers 7%
Air conditioning 6%
Other 32%
2009 Note:
Data from the U.S Geological Survey, U.S Government Printing Office, 2009.
“Other” includes primary aluminum production, continuous casting, chemical processing, and other uses.
Global End Uses of Lithium