In 2008, the primary forms of salt sold or used in the United States were salt in brine 44 percent, rock salt 38 percent, vacuum pan salt 10 percent, and solar salt 8 percent.. Total wor
Trang 1ore output was expected to be in the range of 100 to
105 million metric tons per year by 2010 A further
limited increase in iron-ore production was projected
to the year 2020 without a significant expansion of the
resource base The resource base for iron ore was not
considered profitable for investment because of
taxa-tion issues and technological problems related to
mining and processing the low-grade ores
Other Resources
Russia has many world-class resources other than the
ones described The Noril’sk-Talnakh deposit in
Rus-sia is not only the world’s richest nickel deposit but
also one of the world’s largest platinum-group-metal
and copper deposits Global platinum-group-metal
production and reserves are dominated by South
Af-rica According to Russia’s minister of natural
re-sources, Russia has more than 40 percent of the
world’s platinum-group-metal reserves and almost all
reserves are in mixed sulfide ores at the Noril’sk
com-plex More than 50 percent of Russia’s copper metal
production was produced by Noril’sk Nickel from ore
mined by the company The remainder came from a
much smaller amount of ore mined in the Ural
Moun-tains and a large amount of secondary material
In 1999, Russia ranked sixth in the world in
alu-mina production and eighth in the world in bauxite
output Russia ranked fourth in the world in mine
out-put of antimony in 1999 All antimony reserves are in
the Sakha Republic The only sources of antimony
production are gold antimony quartz vein-type
depos-its, which account for about 50 percent of the
anti-mony reserves
Russia is not only the leading country for available
fossil fuels such as oil, natural gas, and coal, but also a
source of substantial unconventional energy resources,
such as coal-bed methane, peat, and oil shales, which
contain large amount of fuels These resources are
un-economical to exploit at present, but emerging
tech-nologies are being developed to allow for economical
production in the near future Russia is among the
world’s largest peat producers Peat is a natural,
renew-able, organic matter that covers about 4 percent of the
world’s land surface Research shows that peat can
also be converted into methane gas by bacterial
diges-tion or by thermal breakdown at 400°-500° Celsius
Coal-bed methane is being increasingly developed
as a new source of natural gas Russia holds the world’s
largest coal-bed methane resource Methane gas in
coal mines has long been considered potentially risky
Methane explosions have killed tens of thousands
of miners in the world On the other hand, coal-bed methane is viewed as an undeveloped resource Emerging technologies are being developed to sys-tematically extract methane gas from coal seams to be used as energy sources, which would also reduce the likelihood of methane gas explosions in coal mines Over time, coal-bed methane will become an impor-tant energy resource
Yongli Gao
Further Reading
Bradshaw, Michael, et al., eds Essentials of World Re-gional Geography Boston: McGraw-Hill, 2007 Butterman W C., and Earle B Amey III Mineral Com-modity Profiles: Gold Reston, Va.: U.S Geological
Survey, 2005
Craig, James R., David J Vaughan, and Brian J
Skin-ner Resources of the Earth: Origin, Use, and Environ-mental Impact 3d ed Upper Saddle River, N.J.:
Prentice Hall, 2001
De Blij, Harm J., and Peter O Muller Geography: Realms, Regions, and Concepts 13th ed Hoboken,
N.J.: Wiley, 2008
Evans, Anthony M Ore Geology and Industrial Minerals:
An Introduction 3d ed Boston: Blackwell Science,
1993
Levine, Richard M., and Glenn J Wallace “The Min-eral Industries of the Commonwealth of
Indepen-dent States.” In USGS Minerals Yearbook 2005.
Reston, Va.: U.S Geological Survey, 2005
Misra, Kula C Understanding Mineral Deposits Boston:
Kluwer Academic, 2000
Peacock, Kathy Wilson Natural Resources and Sustain-able Development New York: Facts On File, 2008.
Web Sites Central Intelligence Agency The World Factbook: Russia https://www.cia.gov/library/publications/the-world-factbook/geos/rs.html
Energy Information Administration International Energy Data and Analysis for Russia http://tonto.eia.doe.gov/country/
country_energy_data.cfm?fips=RS See also: Chernobyl nuclear accident; Coal; Dia-mond; Gold; Methane; Nickel; Oil and natural gas dis-tribution; Oil and natural gas reservoirs
Trang 2Sagebrush Rebellion
Category: Historical events and movements
Date: Late 1970’s-early 1980’s
The Sagebrush Rebellion was a political movement
that blossomed in the late 1970’s to minimize the
im-pact of federal stewardship over the public lands of the
American West After mixed success, the movement
faded after the election of Republican Ronald Reagan
to the presidency in 1980.
Background
The Sagebrush Rebellion was a political reaction to
a decade of gains for the American environmental
movement as well as an expression of resentment at
the strong federal presence in the states of the
Ameri-can West The federal government owns a large
per-centage of the land in many western states, ranging
from 29 percent of Montana to 85 percent of Nevada
As former Colorado governor Richard Lamm said in
his book The Angry West (1982), the three federal
“superbureaus”—the Bureau of Land Management,
the United States Forest Service, and the National
Park Service—controlled “virtually as much of the
West as the West owns of itself.” Because of this, Lamm
declared, “[W]e cannot control our own destiny.”
The short-term catalyst for the “rebellion” was the
actions of President Jimmy Carter By canceling
fund-ing for eighteen western reclamation projects, Carter
opened himself to charges of federal insensitivity to
the needs of the West Other westerners were
ani-mated by anger over what they viewed as increasing
federal restrictions over the use of public lands In
1979, the Nevada legislature demanded the cession of
20 million federally controlled hectares to the state
Before long, other western public-land states joined
what became known as the Sagebrush Rebellion
Provisions
Carrying the movement to Congress, Senator Orrin
Hatch, a Utah Republican, introduced legislation to
transfer 220 million federal hectares to the control of
thirteen western states The Sagebrush Rebellion
be-came a major issue in the West during the 1980
presi-dential campaign between Carter and Reagan, who announced that he too could be counted “as a rebel.” During the campaign he pledged to pay careful atten-tion to the economic needs of the West Reagan re-marked that “we can turn the Sagebrush Rebellion into the Sagebrush Solution.” When Reagan won the presidency it appeared as though the Sagebrush Re-bellion had a chance for success
However, by the early 1980’s the fires of rebellion were cooling just when the Sagebrush Rebellion ap-peared to have the greatest opportunity for success President Reagan appointed James G Watt as secre-tary of the interior Watt, the former director of the conservative Mountain States Legal Foundation, fa-vored easing restrictions on private-sector exploita-tion of the West’s natural resources Soon Watt leased northern plains coal lands at low prices to private companies This and other actions sparked a resur-gence of environmentalist political concern
Impact on Resource Use
A combination of factors brought the Sagebrush Re-bellion to an end The election of a conservative West-ern president placated many Sagebrush rebels Then
a series of minor scandals, coupled with Watt’s ac-tions, led to a widespread perception that the Reagan administration was giving away the public lands of the West By 1983, Watt and several of his lieutenants had resigned from office amid varying degrees of contro-versy
Steven C Schulte
See also: Bureau of Land Management, U.S.; Carter, Jimmy; Energy politics; Environmental movement; Public lands
Salt
Category: Mineral and other nonliving resources
Where Found Salt (sodium chloride) is widely and abundantly dis-tributed in nature It is present in dissolved form in
Trang 3seawater, salt lakes, and groundwater in various parts
of the world There are also many substantial deposits
of salt in solid form, notably in the United States,
Great Britain, France, Germany, Russia, China, and
India In 2008, the primary forms of salt sold or used
in the United States were salt in brine (44 percent),
rock salt (38 percent), vacuum pan salt (10 percent),
and solar salt (8 percent)
Primary Uses
Salt has numerous uses, chiefly in the chemical
indus-try; metallurgy; ceramics, glass, and glaze
manufac-ture; agriculmanufac-ture; medicine; refrigeration; and foods
In addition to its importance as an industrial raw
ma-terial, salt is an essential nutrient, although its
ubiqui-tous use in commercial food processing has made
over-intake in industrialized nations a major health
concern
Technical Definition
Salt is a general term for naturally occurring sodium
chloride (NaCl) Synonyms include halite, common
salt, and rock salt Its average molecular weight is
58.448 Pure salt may be colorless or white; impurities
may add a yellow, red, blue, or purple tint Its
hard-ness on the Mohs scale is 2 to 2.5 Salt usually occurs as
cubic crystals Its specific gravity is 2.17 It is readily
soluble in water and is insoluble or only slightly
solu-ble in most other liquids It has a melting point of 801°
Celsius and a boiling point of 1,413° Celsius
Description, Distribution, and Forms
Sodium chloride is an important and abundant
inor-ganic chemical It is as essential to life as it is to
mod-ern industry Human blood is composed of 90
per-cent water, 0.9 perper-cent salt, and small amounts of
proteins and other substances As the salt is expended
it must be renewed This fundamental need for salt
has been a driving force behind exploration,
com-merce, and conflict throughout human history Salt
has long been a crucial industrial material as well It
has approximately fourteen thousand different
re-ported uses Total world production of salt in 2008 was
about 260 million metric tons; the United States
ac-counted for about 18 percent of the total
Salt is widely distributed throughout the world and
the geologic column Salt is produced by more than
one hundred nations worldwide; most of them are
able to fulfill their own consumption requirements
from indigenous sources
The world’s largest salt reserve is its oceans, which contain 2.5 percent dissolved salt by weight The oceans are estimated to contain 44 × 1015metric tons
of salt, which would form a cube roughly 18.76 million cubic kilometers in volume Dissolved salt is also pres-ent in salt seas and lakes, such as the Dead Sea in the Middle East, the Aral Sea in central Asia, and the Great Salt Lake in Utah Subsurface brines are other source of dissolved salt These brines can be an-cient seawater that was entrapped in sediments at the time of deposition or saline waters that formed locally
by solution of rock salt beds
Extensive bedded deposits are also found in the form of rock salt These sedimentary deposits occur interbedded with common strata and with other evaporite minerals, such as gypsum and anhydrite The deposits were created as salts precipitated and ac-cumulated on the floor of an ancient landlocked ma-rine body of water Extensive and widespread evapora-tion led to the formaevapora-tion of the deposits, which can reach thicknesses of up to 900 meters Examples of bedded deposits can be found in Michigan, New York, Ohio, New Mexico, Canada, England, and central Eu-rope In North America bedded salt deposits occur mostly in Silurian, Permian, and Triassic formations When vertical or lateral stress is applied to strati-fied salt deposits, the lower-density salt flows plastic-ally through the surrounding higher-density rock to form salt domes These salt domes are usually cylindri-cal in shape and are often capped by anhydrite, gyp-sum, and calcite Sulfur and hydrocarbons are fre-quently associated with salt dome deposits Salt domes are found in Texas, Mississippi, Louisiana, Mexico, Germany, Poland, Romania, Russia, and the Middle East In arid regions salt occurs along with borax, pot-ash, and other evaporite minerals as a surface deposit from desiccated salt lakes Such playa deposits are im-portant in California, Nevada, Utah, and India Salt occurs in nature as halite It is often found interbedded with shale, limestone, dolostone, and rock-gypsum or rock-anhydrite in extensive beds and irregular masses It is frequently associated with gyp-sum, anhydrite, calcite, sylvite, sand, and clay In arid regions it can occur as a white powder, or efflores-cence, on the soil surface It can also be dissolved in the waters of salt springs, salt lakes and seas, and oceans
History Salt manufacture is one of the oldest chemical indus-tries Its availability influenced the locations of cities,
Trang 4Source:Data from the U.S Geological Survey,Mineral Commodity Summaries, 2009 U.S Government Printing Office, 2009.
Metric Tons
Australia
Brazil
Canada
Chile
China
Egypt
France
Germany
India
Iran
Italy
Mexico
Netherlands
Poland
Romania
Russia
Spain
Turkey
Ukraine
United Kingdom
United States
Other countries
12,000,000
7,000,000
12,000,000
5,000,000
60,000,000
2,400,000
6,000,000
19,000,000 15,800,000
2,000,000
2,200,000
8,400,000
5,000,000
4,400,000
2,500,000
2,200,000
4,600,000
2,700,000
5,500,000
5,800,000
46,000,000 29,500,000
Salt: World Production, 2008
Trang 5the migration of populations, and the establishment
of trade routes Salt’s dietary importance led to its
fre-quent use as a universal currency Salt derives its name
from sal, the Latin word for the substance The word
“salary,” which also comes from the Latin term,
re-flects the Roman practice of paying a portion of their
soldiers’ wages with rations of salt
Salt production in the United States began in 1614
with colonists in Virginia, who evaporated seawater to
obtain the resource Extraction of salt from
subsur-face brines began in the United States in 1788 in New
York In 1791, French chemist Nicolas Leblanc
devel-oped a commercial process that used salt to
manufac-ture soda ash The Solvay process, in which salt was
also the chief raw material, supplanted the Leblanc
process in the 1860’s In 1862, the first rock-salt mine
in North America opened at Avery Island, Louisiana
In about 1882, the United States first employed
solu-tion mining methods The 1887 invensolu-tion of the
vac-uum pan was a significant contribution to the salt
in-dustry, as applying a vacuum during evaporation made
water boil at a lower temperature, thereby reducing
the amount of fuel needed to heat the evaporation
pans
Obtaining Salt
Rock salt may be extracted from deposits using
conventional underground mining or solution
mining methods Solution mining involves
intro-ducing pressurized and often heated fresh water
into an injection well drilled into the salt deposit
The water dissolves the salt, and the resulting
brine is pumped back to the surface for mineral
recovery
Whether brines are created by solution mining
or obtained from the ocean, a sea, a lake, or
an-other natural source, they must be evaporated for
their salt contents to be harvested Solar
evapora-tion is effective in areas where the evaporaevapora-tion
rate is high and the precipitation rate low In
many parts of the world, seawater or saline lake
water is pumped into large, specially constructed
ponds, where it is allowed to evaporate naturally
The brine passes through a series of these ponds
during the solar evaporation process In
mechan-ical evaporation, brines are dehydrated in
steam-heated vessels This process is often augmented
by applying a vacuum to make evaporation
pro-ceed at a lower temperature
Desalination, the process of converting salt
water into fresh water, produces salt as a by-product Desalination methods include distillation, membrane osmosis, freezing, and ion exchange Some salt pro-duced by desalination is used in industry
Salt obtained through evaporation is not usually pure sodium chloride Impurities are removed by aer-ation and chemical treatment Small amounts of other substances, such as magnesium carbonate, hy-drated calcium silicate, or tricalcium phosphate, may
be added to prevent lumping Iodized table salt usu-ally contains small amounts of potassium iodide, so-dium carbonate, and soso-dium thiosulfate
Uses of Salt The chief use of salt is as a raw material for the produc-tion of chlorine, sodium metal, and sodium hydrox-ide; it is also an ingredient in the Solvay process for manufacturing soda ash Salt is used in making soaps, textile dyes, lacquers, cements, glass, ceramics, and glazes It is employed in the treatment, smelting, and refining of ores and metals While used as a refrigerat-ing agent, it is also spread in large quantities to melt ice and snow on streets and highways In agriculture, salt is a component of livestock feed, fertilizers, soil amenders, herbicides, and insecticides In the
Chemicals 40%
Deicing 39%
Distributors 8%
Agriculture
& food 6%
Other 7%
Summaries, 2009 Note:
Data from the U.S Geological Survey,
U.S Government Printing Office, 2009.
“Other” includes general industrial and water treatment.
U.S End Uses of Salt
Trang 6cal field, salt is used in pharmaceuticals and specialty
cleansers
Salt is an essential part of human physiology It is
found in most body fluids, such as blood, sweat, and
tears It also provides chlorine for making hydrochloric
acid, a small but vital part of human digestive fluid
Di-etary intake of salt replaces the mineral as it is
con-sumed through normal metabolism The average per
capita consumption of salt is approximately 5.44
kilo-grams a year Salt is widely used as a seasoning for foods,
a curing agent for meats, and a preservative for fish and
other foods While salt is an essential nutrient,
exces-sive amounts in the diet can lead to health
complica-tions Persons suffering from high blood pressure or
heart disease often must restrict the amount of salt in
their diets to avoid aggravating these conditions
Karen N Kähler
Further Reading
Adshead, S A M Salt and Civilization New York: St.
Martin’s Press, 1992
Gevantman, L H., ed Physical Properties Data for Rock
Salt Washington, D.C.: U.S Government Printing
Office, 1981
Jensen, Mead L., and Alan M Bateman Economic
Min-eral Deposits 3d ed New York: Wiley, 1979.
Johnson, K S “Salt Resources and Production in the
United States.” In Industrial Minerals and Extractive
Industry Geology: Based on Papers Presented at the
Com-bined 36th Forum on the Geology of Industrial Minerals
and 11th Extractive Industry Geology Conference, Bath,
England, 7th-12th May, 2000, edited by Peter W.
Scott and Colin M Bristow London: Geological
Society, 2002
Kogel, Jessica Elzea, et al., eds “Salt.” In Industrial
Minerals and Rocks: Commodities, Markets, and Uses.
7th ed Littleton, Colo.: Society for Mining,
Metal-lurgy, and Exploration, 2006
Kurlansky, Mark Salt: A World History New York:
Walker, 2002
MacGregor, Graham A., and Hugh E de Wardener
Salt, Diet and Health—Neptune’s Poisoned Chalice: The
Origins of High Blood Pressure New York: Cambridge
University Press, 1998
Multhauf, Robert P Neptune’s Gift: A History of Common
Salt Baltimore: Johns Hopkins University Press,
1978
Warren, John K “Salt Tectonics.” In Evaporites:
Sedi-ments, Resources, and Hydrocarbons New York:
Springer, 2006
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 Salt: Statistics and Information http://minerals.usgs.gov/minerals/pubs/
commodity/salt See also: Evaporites; Lakes; Oceans; Salt domes; Sed-imentary processes, rocks, and mineral deposits; Soda ash
Salt domes
Category: Geological processes and formations
Salt domes are a major source of the world’s salt Their caprocks are major sources of gypsum and sulfur Up-turned sediments on the flanks of salt domes form stratigraphic traps for oil and natural gas.
Definition Salt domes consist of roughly cylindrical to mush-room-shaped plugs of massive rock salt extending to-ward the Earth’s surface from depths as great as 6,000 meters These salt pillars typically range in diameter from 1 to 3 kilometers; however, some cores reach 12 kilometers in diameter The plug is usually topped by
a limestone, gypsum, and anhydrite caprock
Overview Salt beds, ranging in thickness from a meter to a few hundred meters, are deposited in shallow, hyper-saline, marine environments such as basins of re-stricted circulation in regions where evaporation ex-ceeds precipitation The salt is commonly pure white and is associated with gypsum, anhydrite, and shales Some deeply buried salt beds form mobile salt col-umns that rise toward the surface Salt domes occur in the Colorado-Utah area, the Gulf Coast of the United States and Mexico, Spain, France, Romania, Iran, Ara-bia, and India
Salt domes are emplaced when beds of salt deform plastically under the pressure of overlying rocks and
Trang 7rise through overlying layered
sedi-ments The rising salt forces the
over-lying rocks into domes and punches
through them to leave rock layers
upturned along its flanks The depth
of the salt core beneath the surface
varies widely Deep domes may be
more than 1,750 meters beneath the
surface, but others may expose salt at
the surface As salt reaches near the
surface, it encounters groundwater,
which dissolves the rising salt A
cap-rock of less soluble minerals, mostly
anhydrite, forms on top of the
ris-ing plug Often, anaerobic bacteria
in groundwater break down the
an-hydrite of the caprock, forming
cal-cite and native sulfur in the process
Commercial quantities of sulfur
are dispersed within the caprock of
a few domes Sulfur is extracted from
the caprock by the Frasch process
Water heated to 150° Celsius is
dis-charged into the caprock to melt the
sulfur, and hot air is used to drive it
to the surface The molten sulfur is
then piped to storage, where it
solidi-fies
At shallow domes, anhydrite, gypsum, and
lime-stone in the caprock may be quarried for road metal
or building materials Salt is recovered by
under-ground mining techniques Salt domes account for
only 5 percent of the world’s reserves of salt, but alone
they could supply the world’s demand for thirty
thou-sand years Upturned sedimentary beds around the
flanks of the domes provide traps for oil and gas that
migrate updip and are impounded against the
imper-meable salt The limestone of the caprock also forms a
petroleum reservoir in some salt domes
Cavities may be excavated within salt domes either
by standard mining techniques or by pumping fresh
water into the dome to form a solution cavity The
re-sulting cavity may then be used to store oil or gas
Be-cause salt is impermeable and self-healing when
frac-tured, it has been used as a storage site for nuclear
waste disposal
René A De Hon
See also: Native elements; Nuclear waste and its
dis-posal; Salt
Sand and gravel
Category: Mineral and other nonliving resources
Where Found Sands and gravels are widely distributed on the Earth’s surface; all fifty of the United States have producing de-posits Sand and gravel deposits are not spatially ubiq-uitous, however Sand and gravel are heavy or dense, high in bulk, and low in value, and they cannot be shipped economically for long distances Most sand and gravel in the United States and Canada come from glacial deposits, stream terraces and channels, includ-ing alluvial fans, or from beach deposits of either cur-rent or relict shorelines Some specialty or industrial sands are derived from bedrock when more rigid con-trol over the character of the sand is required
Primary Uses
By far the greatest use of sand and gravel is in con-struction, where they may be employed as fill material
A salt dome is situated in the upper middle section of this portion of the Zagros Moun-tains (NASA)
Trang 8or as the aggregate in concrete Industrial sands are
more specialized, and their uses demand higher
qual-ity Most industrial sand is used to make glass or as
molding sand in foundries The United States
pro-duces more than 1 billion metric tons of construction
sand and gravel and between 25 and 30 million metric
tons of industrial sands
Technical Definition
Sand particles are 0.05 millimeter to 4.76 millimeters
in diameter Gravel particles are larger, 4.76 to 80 or
90 millimeters in diameter Sand fragments are
com-posed almost entirely of single minerals, chiefly quartz,
with significant fractions of feldspars and smaller
pro-portions of mica, chert, and heavy minerals Gravels,
on the other hand, are usually fragments of rocks that
are composed of several minerals Gravels reflect the
geology of the stream basin in which they are located,
because this is the source of the gravel deposit Most
gravels are resistant, but if the source stream basin is
underlain largely by soft sediments, the gravels are
less valuable as a resource Impurities in sand and
gravel deposits consist of silts, clays, or excessive
pro-portions of micas, soft sediments, or rock fragments
that have an undesirable chemistry
Description, Distribution, and Forms
Sand and gravel are the most widely distributed of the
construction aggregates, are the easiest to recover or
mine, and require only simple beneficiation, usually
washing and screening Historically, in the United
States, they have dominated the market for
aggre-gates However, for many purposes, even in rough
construction, they are not as suitable as their closest
competitor—crushed stone or rock—because
sharp-edged broken stones interlock, unlike gravels, which
are rounded by stream transport
Both the quality of a sand or gravel deposit and its
location with respect to market determine the
re-source value of that deposit Quality concerns include
the lithology of the particles (their chemical and
phys-ical character), the size and shape of the particles,
their resistance to abrasion and cracking, the
poten-tial for chemical reactivity, and the freedom of the
de-posit from organic matter, silt, and clay (in other
words, the deposit’s cleanness) Fortunately, most sand
deposits are dominated by quartz particles, which are
both resistant and inert
Gravels can pose a greater problem because of the
variety of rocks in different drainage basins Soft rocks
or those that weather relatively rapidly (shales, friable sandstones, some limestones, and certain metamor-phic rocks, especially schists and slate) do not make valuable gravels A variety of rocks react with the alka-lies in portland cement and must be avoided for that particular use Iron impurities rust, and certain other minerals weather or decompose rapidly These condi-tions lead to weakened construction and are avoided Thus, all gravel deposits are not equally valuable as re-sources, even if they are favorably located with respect
to markets Just as high-quartz sands are more valu-able, so are gravels with high proportions of resistant rocks of the proper chemical composition
Market, in the case of construction sand and gravel,
is defined by population and appropriate construc-tion, such as highways Thus, a sparsely populated re-gion serves as a significant market while interstate highway construction is under way but becomes a small market when the highway is completed The fortunes
of construction sand and gravel suppliers wax and wane with the general economy; boom times of ex-panded residential or office building construction pro-vide an excellent market Recessions with little con-struction activity result in a shrinkage in production The low-value, high-bulk character of sand and gravel dictates that only surface mining is economical (the exception is some higher-value industrial sands, which may be mined underground) Moreover, the mining must be close to metropolitan centers, where most new construction occurs Inevitably, the urban centers grow and encounter the sand and gravel min-ing Zoning may then displace the mining to more re-mote locations because of complaints about dust, noise, truck traffic, or the unsightliness of gravel pits Restrictions on the use of wetlands are increasing, particularly in cases in which endangered species may
be involved There is also an increasing concern with silica dust, which may affect specialty industrial sands
History
A measure of the overall relationship between popu-lation numbers and construction may be seen in the history of sand and gravel production in the United States During the Depression of the 1930’s annual production was about 180 million metric tons In
1946, before widespread construction began in the postwar era, production was about 230 million metric tons By 1960 construction had expanded significantly and production stood at 641 million metric tons In
1970, residential construction and the interstate
Trang 9high-way program were active; production was about 856
million metric tons By 1994, although population
had grown, highway and commercial construction
had declined, and total sand and gravel production
was just more than 918 million metric tons, of which
about 27 million metric tons were industrial sands By
2008, U.S production of sand and gravel for
construc-tion was about 1 million metric tons; for industrial
use, about 30 million metric tons Throughout the
post-World War II period, metropolitan population
concentrations were far more important as markets
for construction sand and gravel than were rural
re-gions, which generally failed to generate construction
in proportion to their population numbers The
ma-jor exception to this generalization is the interstate
highway construction program, which generated
tem-porary markets for sand and gravel in even the most
sparsely settled portions of the country
Obtaining Sand and Gravel
Nearly all gravel deposits, and most sand deposits, are
found in stream sediments Present-day stream
depos-its include channels, low terraces, and active portions
of alluvial fans Under these circumstances, sands
and gravels removed by dredging or open-pit mining
may be renewed by recurrent flooding or high
stream-flows Relict stream deposits are those created by
gla-ciation, including outwash fans and valley train
depos-its (the latter extending to the oceans from the glacial
source), as well as relatively minor sources such as
eskers, kames, and moraines deposited close to the ice
margin Most alluvial fans in western North America
are also relict or inactive in that they were formed
dur-ing the Pleistocene era and are not renewed by
cur-rent geologic processes In either case, virtually all
sand and gravel are found in surficial deposits, which
are frequently wetlands This fact has advantages in
terms of mining costs, but it also results in
environ-mental problems and land-use conflicts
Uses of Sand and Gravel
The overwhelming use of sand and gravel is in
con-struction Use of these materials for fill, base, or
subgrade of highways is the least demanding of
qual-ity requirements, and sand and gravel may not even
be washed or screened for these uses Usage in
con-crete, however, is far more demanding, both in terms
of size-of-particle requirements (sorting, screening,
or crushing may be used to produce the desired size)
and in terms of quality (avoiding easily weathered or
alkali-reactant rocks) Substitutes for sand and gravel
in construction are crushed stone or rock and light-weight aggregates Lightlight-weight aggregates, largely vol-canic rocks, are increasingly employed in specialty concretes and building blocks Crushed rock is uti-lized where more rigid specifications for concrete ex-ist or in regions where sand and gravel are scarce (this high-bulk, low-value commodity is shipped largely by truck, and rarely for distances greater than 30 me-ters)
Industrial sand and gravel encompass a variety of uses, each with its own specifications as to desirable characteristics in the product and its own market— hence the resultant location of mining activities Glassmaking and foundry or molding sands lead the list of uses by tonnage; the former requires more rigid specifications and is located where construction is ac-tive, and the latter is located where metalworking is significant The petroleum industry uses significant quantities for hydraulic fracturing of oil and gas wells Abrasives, especially for blast sands, also rank high
Concrete aggregates 44%
Roads 23%
Construction fill 14%
Asphaltic aggregates 12%
Other 7%
Commodity Summaries, 2009 Note:
Data from the U.S Geological Survey,
U.S Government Printing Office, 2009.
“Other” includes plaster and gunite sands, blocks, bricks, pipes, filtration, golf courses, railroad ballast, roofing granules, and snow and ice mitigation.
U.S End Uses of Construction
Sand and Gravel
Trang 10Each use or type of sand has competition from
substi-tutes that may reduce the resource value of deposits or
the profitability of an industry Glass, for example, has
largely been replaced by aluminum and plastics as the
material for containers in the food and beverage
in-dustry Abrasives have come under fire for reasons of
health, such as the breathing of dust by workers
Neil E Salisbury
Further Reading
Bell, Fred J., and Laurance J Donnelly “Gravel, Sand,
and Clay Pits.” In Mining and Its Impact on the
Envi-ronment New York: Taylor & Francis, 2006.
Evans, Anthony M An Introduction to Economic Geology
and Its Environmental Impact Malden, Mass.:
Black-well Science, 1997
Gyr, Albert, and Klaus Hoyer Sediment Transport: A
Geophysical Phenomenon Dordrecht, the
Nether-lands: Springer, 2006
Hamilton, W N., and W A D Edwards “Industrial
Minerals in Western Canada Sedimentary Basin.”
In Industrial Minerals and Extractive Industry Geology:
Based on Papers Presented at the Combined 36th Forum
on the Geology of Industrial Minerals and 11th
Extrac-tive Industry Geology Conference, Bath, England,
7th-12th May, 2000, edited by Peter W Scott and Colin
M Bristow London: Geological Society, 2002
Harben, Peter W., and Robert L Bates Geology of the
Nonmetallics New York: Metals Bulletin, 1984.
Kogel, Jessica Elzea, et al., eds “Industrial Sand and
Sandstone.” In Industrial Minerals and Rocks:
Com-modities, Markets, and Uses 7th ed Littleton, Colo.:
Society for Mining, Metallurgy, and Exploration,
2006
Smith, M R., and L Collis, eds Aggregates: Sand,
Gravel, and Crushed Rock Aggregates for Construction
Purposes 3d ed Revised by P G Fookes et al
Lon-don: Geological Society, 2001
Web Sites
U.S Geological Survey
Construction Sand and Gravel: Statistics and
Information
http://minerals.usgs.gov/minerals/pubs/
commodity/sand_&_gravel_construction
U.S Geological Survey
Silica: Statistics and Information
http://minerals.usgs.gov/minerals/pubs/
commodity/silica
See also: Abrasives; Aggregates; Cement and con-crete; Glaciation; Glass; Streams and rivers; Surface Mining Control and Reclamation Act; Wetlands
Sandstone
Category: Mineral and other nonliving resources
Where Found Sandstone is found throughout the world It is proba-bly the most familiar, but not the most abundant, of all sedimentary rock, that group of rocks composed of consolidated rock fragments of all sizes
Primary Uses Sandstone has numerous uses in the construction in-dustry It is used to make bricks, concrete, and plaster
Technical Definition Sandstone is a rock composed of abundant rounded
or angular, sand-size fragments derived by the disinte-gration of existing rock The sand fragments are com-monly cemented together by calcium carbonate, sil-ica dioxide, or iron oxide
Description, Distribution, and Forms
In chemical composition, the average sandstone is principally composed of approximately 80 percent sil-ica dioxide, 6 percent aluminum oxide, and 3 percent each calcium oxide and carbon dioxide Arkose is a sandstone that contains fairly large, angular granules
of pink feldspar In North America two economically significant sandstones are the Oriskany sandstone of New York State and the Saint Peter sandstone of Min-nesota Both these sandstones are important as glass sand and natural gas reservoir rock
Sandstones of a wide variety of physical characteris-tics and mineral compositions are known While many sandstone classification schemes exist, a common scheme lists four typical varieties The chief constitu-ent (90 percconstitu-ent or greater) of siliceous sandstone is the mineral quartz, whereas more than 25 percent of arkose is composed of the mineral feldspar A third va-riety is graywacke, a heterogeneous mixture of quartz and feldspar surrounded by fine-grained clay mate-rial In regions of volcanic activity, accumulations of sand-size detritus ejected from active volcanoes form tuffaceous sandstone