Geological Survey Dimension Stone: Statistics and Information http://minerals.usgs.gov/minerals/pubs/ commodity/stone_dimension See also: Aggregates; Calcium compounds; Carbon-ate minera
Trang 1the necessary equipment, and a flick of a switch rather
than a large engine and the inconvenient (often
dan-gerous) belts used to transfer power to various pieces
of equipment
Energy efficiency and materials efficiency grow as
technology evolves Often, increased efficiency is
sim-ply a by-product of increased production or quality
Each doubling of cumulative production tends to
drop production costs, including energy costs, by 20
percent These improvements are connected to
con-trol of heat, concon-trol of motion, and the development
of entirely new processes
Heat
Heat is the greatest component of manufacturing
en-ergy use Heat (or the removal of heat) involves the
same issues that space conditioning of a home does
One can add more fuel or reduce losses through
in-creased efficiency Efficiency can be inin-creased by
hav-ing more insulation in the walls, a furnace that burns more completely, a furnace that uses exhaust gases to preheat air coming into it, a stove with a lighter rather than a pilot light, and controls that shut off heat to un-used areas
Manufacturing has the additional option of selling excess heat or buying low-grade heat for cogener-ation Often a manufacturing plant only needs low-grade heat of several hundred degrees for drying or curing materials This heat production does not fully use the energy of the fuel An electrical power plant running at 600° Celsius can generate electricity and then send its “waste heat” on to the industrial process
A manufacturing plant also applies energy to mate-rials, and in these processes there are many choices Heat may be applied in an oven (large or small) Some energy may also be applied directly For in-stance, oven curing of paint on car parts has been re-placed by infrared (“heat lamp”) radiation for quicker
A worker at the Kawasaki manufacturing plant in New York assembles a New York City subway car Industrial manufacturing accounts for a significant portion of the energy used in the United States (AP/Wide World Photos)
Trang 2production Some high-performance aerospace
al-loys are heated by microwave radiation in vacuum
chambers
There are a variety of other energy-saving
ap-proaches Automated process controls are a major
en-ergy saver In chemical industries, separating
materi-als by their different boiling points with distillation
columns requires much less steam than other
meth-ods Also, the continuous safety flames at refineries
are being replaced by automated lighters
Another energy-efficient technique is to combine
processes For instance, steelmaking often comprises
three separate heating steps: refining ore into blocks
of pig iron, refining that into steel, and then forming
the steel into products, such as I beams or wire An
in-tegrated steel mill heats the materials only once to
make the finished product A steel “minimill” tends to
be smaller, uses expensive electricity, and goes only a
short distance in the production process—from iron
scrap to steel On the other hand, the minimill is
recy-cling a resource, thereby saving both energy and
ma-terials The recycling of paper, plastics, and some
met-als typically requires one-half the energy needed to
produce virgin materials The fraction for aluminum
is about one-fourth
Motion
Cutting, grinding, pumping, moving, polishing,
com-pressing, and many other processes control the
mo-tion of materials and of heat They use less energy
than heating, but they often represent the high-grade
energy in electricity
Eighty percent of the electricity used by industry is
used for motors Motors can be made efficient in
many ways, including controllers that match power
use to the actual load, metal cores that drop and take
electric charges more easily, and windings with more
turns of wire Easing the tasks of industrial motors
re-quires many disciplines For example, fixing nitrogen
into ammonia (NH3) is typically done with streams of
nitrogen and hydrogen passing over a catalyst An
im-proved catalyst pattern increases the reaction rate and
thus decreases the hydrogen and nitrogen pumping
Automated controls again can control pumping,
us-ing it only where and when it is needed
Reducing Energy Use
Several processes can reduce energy use For
exam-ple, a lower-pressure process for making polyethylene
plastic uses one-fourth of the energy used in the
previ-ous process Plastics have replaced energy-intensive metals in many commercial products Silica in fiber-optic cables is replacing copper for communications Composites, made with plastics and glass, metal, or other plastic fibers, not only require less energy to fab-ricate than all-metal materials but also have greater capabilities Composites in railroad cars and airplanes reduce weight and thus energy costs of operation Vacuum deposition of metals, ceramics, and even diamond provide cheaply attained materials that mul-tiply savings throughout industry Diamond-edged machine tools operate significantly faster or longer before replacement Rubidium-coated heat exchang-ers withstand sulfuric acid formed when the exhaust from the burning of high-sulfur coal drops below the boiling point, which allows both harnessing that lower heat and recovering the sulfur
Other new processes have been contingent on de-velopments in entirely new, even radical, fields In
Engines of Creation (1986), K Eric Drexler discussed
the concept of “nanotechnology,” proposing micro-scopic robots small enough to build or repair objects one molecule at a time The “nanobytes” could manu-facture items with unprecedented strength and light-ness Today society already sees the benefits of the miniaturization of nanotechnology in areas such as the electronics industry The continuing improve-ment in data storage and processing speed made possible by smaller parts is just one example Genetic engineering reduces energy costs in the chemical in-dustry Parasitic bacteria on legumes (such as peanuts and soy beans) fix atmospheric nitrogen into chemi-cals the plants can use Breeding similar bacteria for other crops can largely eliminate the need for ammo-nia fertilizer (and thereby decrease nitrate runoff )
Economics and Efficiency Costs are the biggest factor affecting energy efficiency
in manufacturing When the price of natural gas was fixed by law at a low rate, for example, steam lines in some chemical plants had no insulation—it simply was not cost-effective to insulate
Even after prices rise, there is often a long time lag For example, the use of bigger pipes in a chemical plant means lower pumping costs, but the cost of in-stalling big pipes is not justified when energy costs are low When energy costs rise, new plants being built might use the larger pipes, but old plants might well run for many years before replacement or a major refit
Trang 3Similarly, highly efficient electrical motors are only
about 25 percent more costly than conventional
mo-tors and are able to return the extra cost and start
gen-erating profit within three years However, rebuilt
conventional motors are available for one-third of the
price of new motors Thus the investment in efficient
new motors might not pay for itself for several
addi-tional years
Finally, social and political factors affect the
adop-tion of energy-efficient technologies Government
policies have often discouraged recycling by granting
tax subsidies to raw materials production and
estab-lishing requirements for their use rather than
recy-cled materials Tax policies have not allowed enough
depreciation to encourage long-term investments in
energy efficiency
Government policies and programs can lead the
way to decreased energy use in manufacturing The
U.S Department of Energy, for example, supports
the Save Energy Now program to partner with
compa-nies and provide an energy-use assessment at no cost
to the participating company This results in
recom-mendations for how the company can reduce its
en-ergy consumption in the manufacturing process as
well as in energy use in the workplace Such programs
on a global scale can make industry adopt a more
energy-efficient manufacturing process
Roger V Carlson
Further Reading
Beer, Jeroen de Potential for Industrial Energy-Efficiency
Improvement in the Long Term Boston: Kluwer
Aca-demic, 2000
Drexler, K Eric Engines of Creation: The Coming Era of
Nanotechnology New York: Anchor Books, 1990.
Gopalakrishan, Bhaskaram, et al “Industrial Energy
Efficiency.” In Environmentally Conscious
Manufac-turing, edited by Myer Kutz Hoboken, N.J.: Wiley,
2007
International Energy Agency Tracking Industrial
En-ergy Efficiency and CO 2 Emissions: In Support of the G8
Plan of Action—Energy Indicators Paris: Author,
2007
Kenney, W F Energy Conservation in the Process
Indus-tries Orlando, Fla.: Academic Press, 1984.
Larson, Eric D., Marc H Ross, and Robert H
Wil-liams “Beyond the Era of Materials.” Scientific
Amer-ican 254, no 6 (June, 1986): 34.
National Research Council Decreasing Energy Intensity
in Manufacturing: Assessing the Strategies and Future
Directions of the Industrial Technologies Program Wash -ington, D.C.: National Academies Press, 2004 Ross, Marc H., and Daniel Steinmeyer “Energy for
In-dustry.” Scientific American 263, no 3 (September,
1990): 89
Web Site U.S Department of Energy Industrial Technologies Program http://www1.eere.energy.gov/industry See also: Buildings and appliances, energy-efficient; Electrical power; Energy economics; Energy politics; Genetic prospecting; Industrial Revolution and in-dustrialization; Petrochemical products; Recycling; Steel
Marble
Category: Mineral and other nonliving resources
Where Found Marbles, geologically defined as metamorphically al-tered calcareous rocks, are found in the core areas of younger mountain chains formed by the collision of tectonic plates and the consequent uplift and distor-tion of carbonate sedimentary strata They are also found in the exposed roots of ancient, very eroded mountain chains of continental shield areas Impor-tant marble-producing areas include the Carrara area
in the Italian Apennines and Vermont, Georgia, and Alabama in the United States
Primary Uses Marble is used in architecture as both an ornamental and a structural stone It is also used as an artistic me-dium for three-dimensional art such as sculpture, in-terior furnishings, and mortuary and historical mon-uments
Technical Definition Geologists define marble as a type of rock produced
by metamorphic processes acting on either limestone
or dolomite (dolostone), causing recrystallization through heat and pressure to produce a coarser-grained, harder rock Stonemasons and quarriers have
a more generic definition, which calls almost any hard rock that accepts a fine polish marble
Trang 4Description, Distribution, and Forms
As defined geologically, marble is a type of rock
com-posed primarily of calcite It can be, like limestone,
monomineralic in nature—that is, a rock composed
of only one, or nearly one, mineral Thus it can be
up to 99 percent calcite (calcium carbonate) True
marble can be derived from either limestone or
dolo-mite (sometimes called dolostone) Dolodolo-mite
(cal-cium magnesium carbonate) is a carbonate rock in
which much, if not most, of the original calcium
carbonate has been replaced by magnesium True
marbles are formed by two types of metamorphism:
regional and contact Regional metamorphism is
usu-ally tectonic in nature and involves the slow
com-pression and heating of rocks by large-scale crustal
movements of the Earth over long periods of time
Contact metamorphism is caused by rocks coming
into contact, or near contact, with sources of great
geologic heat, such as intruding
bod-ies of magma; in these cases change
can be effected within a short period
of time
History
Marble in its various forms has been
known and admired since remote
antiquity as a stone of choice for
many applications Some of the
earli-est known works of true
architec-ture that have survived from ancient
Mesopotamia, Egypt, and Greece
fea-tured marble as either decorative or
structural elements Sculptures,
bas-reliefs, dedicatory columns, and
tri-umphal arches have frequently
fea-tured various marbles Thus marble
has been in use at least five thousand
years, dating back to the first
civili-zations, and its use continues up to
the present Many sculptors through
the ages—among them such giants
as Michelangelo, working in the
fif-teenth and sixfif-teenth centuries in
Italy—have preferred marble,
espe-cially the pure white varieties
Obtaining Marble
Marble deposits are quarried in large
operations that may involve
hun-dreds of workers In Europe marble
is often obtained from quarries that have been worked continuously since antiquity Until the last century or
so, work was laboriously performed with age-old tradi-tional tools and methods, but with the advent of power equipment the methodology and speed of ex-traction have greatly improved Some constants have remained, such as the general strategy regarding ex-traction of large blocks of marble: removing the over-burden (overlying sediments and rubble, if any), defin-ing a quarry floor and front by quarrydefin-ing monolithic blocks of marble parallel to their natural jointing planes, cutting away large blocks on all sides and moving the marble to the quarry floor, trimming, re-moving the marble from the quarry, and transporting
it to the purchaser (often by use of specially built rail-road systems)
Marble extraction has never had significant envi-ronmental effects, as the true marbles are chemically
White marble is quarried from this site in Ticino, Switzerland (Karl
Mathis/Key-stone/Landov)
Trang 5inert for all practical purposes The metamorphism
they underwent in their natural development
stabi-lized their constituent minerals, including the trace
minerals such as iron and magnesium from which
col-ored marbles derive their patterns and hues
Uses of Marble
The primary importance of marble is its use in
archi-tectural columns, floorings, wall coverings, sculpture,
vases and other receptacles, and monuments of all
sorts Beginning in the twentieth century, new minor
uses were found for marble, including electrical
out-let baseplates and other electrical insulators, as it is a
good natural insulator
Frederick M Surowiec
Further Reading
Dietrich, R V., and Brian J Skinner Gems, Granites,
and Gravels: Knowing and Using Rocks and Minerals.
New York: Cambridge University Press, 1990
Kogel, Jessica Elzea, et al., eds “Decorative Stone” and
“Dimension Stone.” In Industrial Minerals and
Rocks: Commodities, Markets, and Uses 7th ed
Little-ton, Colo.: Society for Mining, Metallurgy, and
Ex-ploration, 2006
Mannoni, Luciana, and Tiziano Mannoni Marble: The
History of a Culture New York: Facts On File, 1985.
Pellant, Chris Rocks and Minerals 2d American ed.
New York: Dorling Kindersley, 2002
Price, Monica T The Sourcebook of Decorative Stone: An
Il-lustrated Identification Guide Buffalo, N.Y.: Firefly
Books, 2007
Robinson, George W Minerals: An Illustrated
Explora-tion of the Dynamic World of Minerals and Their
Prop-erties Photography by Jeffrey A Scovil New York:
Simon & Schuster, 1994
Schumann, Walter Handbook of Rocks, Minerals, and
Gemstones Translated by R Bradshaw and K A G.
Mills Boston: Houghton Mifflin, 1993
Web Sites
U.S Geological Survey
Crushed Stone: Statistics and Information
http://minerals.usgs.gov/minerals/pubs/
commodity/stone_crushed
U.S Geological Survey
Dimension Stone: Statistics and Information
http://minerals.usgs.gov/minerals/pubs/
commodity/stone_dimension
See also: Aggregates; Calcium compounds; Carbon-ate minerals; Gypsum; Lime; Limestone; Metamor-phic processes, rocks, and mineral deposits
Marine mining
Category: Obtaining and using resources
The oceans cover 71 percent of the Earth’s surface, and they represent a vast, largely untapped reservoir of nat-ural resources With advancements in imaging and other technologies, efforts to locate and retrieve the vast variety of mineral resources have expanded, although they continue to be mitigated by economic, ecological, and political offsets.
Background Ocean mining represents only a small percentage of the total mining done worldwide, because land depos-its are more easily recognized and obtained than underwater deposits Until the 1970’s, deep-ocean de-posits could not be mined commercially because pre-cise navigation to survey deposits and guide dredges did not exist Since then, ocean technologies have im-proved significantly Moreover, competing land de-posits are used (or paved over), and expanding econ-omies are increasing demand Thus the “mines of Neptune” are ripe for use Marine mining can be di-vided into three categories: mining seawater, extend-ing land minextend-ing along the continental shelves, and mining the ocean floors
Mining Seawater Seawater can be seen as a massive ore body contain-ing mostly water with an assortment of dissolved min-erals If seawater processing were efficient enough, more than sixty elements could be extracted The major constituents of seawater are water (H2O, 96.5 percent), sodium chloride (NaCl, 2.3 percent), mag-nesium chloride (MgCl2, 0.5 percent), sodium sul-fate (Na2SO4, 0.4 percent), and calcium chloride (CaCl2, 0.1 percent)
Sodium chloride, or table salt, has been evapo-rated from seawater since antiquity, with sunlight and wind supplying the energy for the process Modern table salt extraction begins with seawater in evapora-tion ponds that appear somewhat similar to those that have been used for centuries However, the old
Trang 6step pond has been replaced by several ponds A first
pond settles out mud, iron salts, and calcium salts At
a second pond, slaked lime (calcium hydroxide,
Ca(OH)2) takes sulfur ions and precipitates out as
gypsum plaster (calcium sulfate, CaSO4) The table
salt precipitates at a third pond, leaving a brine rich in
salts of magnesium and potassium
Magnesium was first extracted commercially in
World War II One method uses sea shells (calcium
carbonate) baked to drive off carbon dioxide Adding
water produces (again) calcium hydroxide, from
which the hydroxide combines with magnesium and
precipitates out Later, the precipitate is combined
with hydrochloric acid (HCl), making magnesium
chloride, which can be separated by electrolysis
Other systems go to magnesium carbonate (MgCO3)
or magnesium oxide (MgO) Bromine-rich brine is
treated with acid to get elemental bromine A similar
process produces iodine
Shellfish naturally extract calcium from seawater
by growing (accreting) calcium carbonate (CaCO3)
This process can be mimicked by electrical accretion,
in which a weak electrical charge on a wire screen
accretes calcium carbonate, gradually making a sheet
of artificial limestone while metal at the opposite
elec-trode dissolves Calcium carbonate accretion is
exper-imental and expensive However, it allows one to
“grow” structures on site, and it may someday be used
to build major oceanic structures
Water, of course, is the prime constituent of
seawa-ter, and desalination (removal of salt from seawater or
other salt solutions) was performed commercially
be-ginning in the 1960’s The water and salts can be
sepa-rated by distillation (much as evaporation and rain
perform distillation in the hydrologic cycle), by
low-pressure distillation (in which the water boils at lower
temperatures), by refrigeration (in which ice freezes
fresh, leaving concentrated brine), and by osmotic
separation (in which pressure or electricity pulls water
through a membrane, leaving concentrated brine)
However, desalination is always expensive, and
natu-ral water sources are cheaper except in desert
coun-tries
Extracting other minerals from seawater is
theoret-ical Although a cubic kilometer of seawater contains
metric tons of many elements, those metric tons can
be obtained only by pumping the water through some
extraction process The pumps and extraction
pro-cess usually cost more than the extracted material is
worth After World War I, renowned German chemist
Fritz Haber tried to extract gold from seawater to pay his nation’s war debts but met with no success Like-wise, filtering for uranium has failed Only plants and animals may be able to do such type of extractions: Certain shellfish and worms in the oceans are able to concentrate minerals hundreds or even thousands of times more than they are concentrated in the sur-rounding ocean
Deposits on the Continental Shelf Where the continents meet the oceans, they generally slope gently for some distance before plunging into deep ocean waters Worldwide, this shallow continua-tion (down to roughly 200 meters), called the conti-nental shelf, covers an area equivalent to that of Af-rica
Typical land minerals continue outward under the water on the continental shelf In addition, the conti-nental shelf has water-sorted deposits called placers along continuations of rivers “drowned” by changes
in sea level and along beaches Furthermore, many coastlines are somewhat like a set of stairs with drowned beaches and old beaches above the water line
Tunnel mines have been extended from shore to obtain particularly desired ores, such as tin off En-gland and coal off Japan The Japanese have built arti-ficial islands and tunneled from them to the sur-rounding deposits Such methods can be extended However, dredging is now the most common method
of mining shallow deposits A suction dredge (essen-tially a giant vacuum cleaner) can operate well to roughly 30 meters Below that, economics shift toward lines of buckets or other exotic means
The most commonly dredged materials are sand and gravel Shells and coral are also dredged These are cheap materials per unit, but the vast tonnage makes them important More valuable ores are dredged in smaller tonnages throughout the world For instance, gold is dredged off Alaska, and dia-monds are dredged off the west coast of South Africa Tin ore is dredged off Southeast Asia, and iron and ti-tanium ores are mined off Australia
Deep Ocean Deposits The deeper waters of the ocean contain potential re-sources beyond imagining To take only one example, the phosphorus-containing minerals glauconite and phosphorite, starting at the edge of the continental shelf, can easily be processed for fertilizer
Trang 7In tectonically active areas, water seeping down
near volcanic rock is heated and eventually expelled
back into the ocean These hydrothermal vents, or
marine vents, carry dissolved minerals, usually
sul-fides of zinc, lead, copper, and silver, along with lesser
but still significant amounts of lead, cadmium, cobalt,
and gold Such deposits have been test mined in the
Red Sea (where underwater valleys keep rich muds
enclosed) In the deep ocean, such deposits make
chimneys of metal sulfides that might eventually be
mined
The greatest deposits are in the deep ocean away
from land Rocks, sharks’ teeth, and even old spark
plugs provide settling points for the accretion of
so-called ferromanganese nodules, which are oxides of
mostly iron and manganese that also contain
poten-tially profitable small amounts of copper, nickel, and
cobalt These potato-shaped ores cover millions of
square kilometers and comprise billions of metric
tons of metal
Economics, Ecology, and Politics
The difference between potential resources and what
are termed mineral “reserves” is what people are
will-ing to do and what it will cost to obtain them This is
particularly true of marine mining The cost of
shal-low dredging is cheaper than land mining, but the
ad-vantage rapidly disappears as the waters grow deeper
and the distance to the processing plant on shore
be-comes greater For example, deep-ocean mining of
ferromanganese nodules for copper might be much
closer to reality if fiber-optics technology had not cut
into the applications for copper cables Finally,
min-ing deep-sea ferromanganese nodules might yield the
greatest profits from the small amounts of copper and
nickel However, ocean mining could also saturate the
markets for cobalt and manganese, with unknown
consequences—cobalt might directly replace nickel
in stainless steel, making the stainless steel a cheaper
competitor of copper
Ecological concerns include the fact that dredging
releases tremendous clouds of silt, killing wildlife
and causing shallow waters to lose fish production
Dredging in cold, deep-ocean waters is worse,
damag-ing areas of sparse, slowly reproducdamag-ing life that
re-quire decades to heal New types of neat dredges may
be required if deep-ocean deposits are ever to be used
commercially
Politics is an even more powerful part of the
pic-ture A political decision that required coal-burning
plants on land to reduce emissions of sulfur oxide and sulfate created a glut of recovered sulfur That glut largely destroyed offshore sulfur mining Phosphorite mining off the California coast was canceled after it was discovered that the area had been used for dump-ing old bombs and shells Tax incentives for recycldump-ing might delay the need for deep-ocean mining by de-cades, or requirements for electric cars might push ferromanganese-nodule mining forward in order to obtain nickel for batteries Deep-sea mining controls from the Law of the Sea Treaty would prevent rival mining dredges from colliding, but the costs of future deep-ocean mining would probably include undeter-mined taxes and subsidies to potential mining rivals
Roger V Carlson
Further Reading
Borgese, Elisabeth Mann The Mines of Neptune: Min-erals and Metals from the Sea New York: H N.
Abrams, 1985
Cronan, David S., ed Handbook of Marine Mineral De-posits Boca Raton, Fla.: CRC Press, 2000.
Earney, Fillmore C F Marine Mineral Resources New
York: Routledge, 1990
Shusterich, Kurt Michael Resource Management and the Oceans: The Political Economy of Deep Seabed Mining.
Boulder, Colo.: Westview Press, 1982
United Nations Division for Ocean Affairs and the
Law of the Sea Marine Mineral Resources: Scientific Advances and Economic Perspectives New York:
Au-thor, 2004
See also: Deep drilling projects; Desalination plants and technology; Integrated Ocean Drilling Program; Law of the sea; Manganese; Marine vents; Oceans; Oil and natural gas drilling and wells
Marine vents
Category: Geological processes and formations
Marine vents are localized areas of the seafloor where cold seawater interacts with magma The result of this interaction produces spectacular eruptions of hot sea-water and enables the precipitation of sulfide minerals
of iron, copper, and zinc.
Trang 8Marine vents, more commonly known as deep-sea
hy-drothermal vents, are produced along deep fractures
in the seafloor These fractures are associated with the
mid-ocean ridges The mid-ocean ridges are undersea
mountain ranges that are sites of active volcanism
De-spite their association with undersea volcanic
moun-tain ranges, all marine vents occur at depths greater
than 2 kilometers below the surface Marine vents are
studied primarily by deep submersible vehicles
Overview
Marine vents are formed when fractures in the
sea-floor develop and cold water flows in from above As
the seawater flows deeper into the fractures, it may
en-counter rocks heated by close proximity to magma;
the rocks heat the seawater The heated water begins
to dissolve minerals from the surrounding rocks, and
its chemistry changes from that of common seawater
If a critical temperature is reached, the hot water will
rush to the surface Although their appearance
sug-gests an explosive volcanic eruption on land, marine
vents are more like geysers than volcanoes
As the hot seawater exits the vent, it begins to cool
rapidly Minerals which are in solution begin to
pre-cipitate out This precipitation may give a dark, smoky
appearance to the hot water exiting the marine vent
The name “black smoker” is commonly applied to
these vents The minerals which commonly
precipi-tate out in these vents are metal sulfides
(combina-tions of a metal and sulfur) The most common
min-erals found are sulfides of iron, copper, and zinc
These minerals form crusts around the opening and
may precipitate into a tall “chimney” of minerals
around the marine vent
Marine vents are also the site of unique biologic
communities These communities thrive in the total
absence of sunlight The food chain is based on
bacte-ria that derive their energy from chemosynthesis This
process enables the bacteria to derive their energy
from chemicals dissolved in the hot water exiting the
marine vents Other animals depend on the bacteria
Some animals associated with the vent communities
grow to very large sizes Tube worms around marine
vents may be larger than 3 meters in length Because
the communities depend on the vent waters for their
source of energy, the animals live closely packed
around the vent When vents become inactive, the
communities die While not a likely source of food for
humans, it has been suggested that the vent animals
may contain unusual chemicals which may help de-velop new medicines
There is a great deal of difficulty and expense in-volved in reaching deep marine vents This fact, plus the cost of bringing minerals and animals to the sur-face and shipping them to shore, must be considered
in deciding whether it is feasible to use these valuable resources Despite the obstacles, marine vents remain the focus of much geologic, biologic, and oceano-graphic research
Richard H Fluegeman, Jr.
See also: Biodiversity; Copper; Hydrothermal solu-tions and mineralization; Iron; Oceanography; Sea-floor spreading; Zinc
Mercury
Category: Mineral and other nonliving resources
Where Found Mercury is generally found associated with volcanic rocks that have formed near subduction zones The primary producing areas are in China, Kyrgyzstan, Spain, and Russia
Primary Uses Mercury is used in the industrial production of chlo-rine and caustic soda It is also used in dry cell batter-ies, paints, dental amalgams, gold mining, scientific measuring instruments, and mercury vapor lamps Several of these uses are now banned in the United States
Technical Definition Mercury (chemical symbol Hg) is a silvery white metal that belongs to Group IIB (the zinc group) of the peri-odic table It has an atomic number of 80 and an atomic weight of 200.5 It has seven stable isotopes and a density of 13.6 grams per cubic centimeter Also known as quicksilver, mercury has a melting point of
−38.87° Celsius, making it the only metal that is liquid
at normal room temperature It boils at a temperature
of 356.9° Celsius and has a constant rate of expansion throughout the entire range of temperature of the liq-uid Mercury alloys with most metals and is a good conductor of electricity
Trang 9Description, Distribution, and Forms
Mercury is a relatively scarce element on Earth,
ac-counting for only 3 parts per billion in crustal rocks It
is found both as free liquid metal and, more
com-monly, as the sulfide mineral cinnabar (HgS) It is
generally found in areas of past volcanic activity
Mer-cury compounds are formed from merMer-cury with
ei-ther a +1 or +2 oxidation state The most common
mercury (I) compound is mercury chloride (Hg2Cl2),
and the most common mercury (II) compounds are
mercury oxide (HgO), mercury bichloride (HgCl2),
and mercury sulfide (HgS) (The Roman numerals
refer to the valence state of the mercury.)
Mercury forms compounds that are used in
agri-culture, industry, and medicine Some organic
mer-cury compounds, such as phenylmermer-cury acetate, are
used in agriculture as fungicides to control seed rot,
for spraying trees, and for controlling weeds Because
of their highly toxic nature, care must be used when
applying or using such mercury compounds
Mercury is a rare crustal element that is found both
as liquid elemental mercury and combined with other
elements in more than twenty-five minerals Cinnabar
is the primary ore mineral of mercury, and it is
generally found in volcanic rocks and
occa-sionally in associated sedimentary rocks The
volcanic rocks were generally formed as
volca-nic island arc systems near subduction zones
Since the deposits are concentrated in faulted
and fractured rocks that were formed at or
near the surface, they are extremely
suscepti-ble to erosion Mercury is a highly volatile
ele-ment, and it is usually lost to the atmosphere
during the erosion of the ore deposits
Mercury is also an extremely toxic element
that can be easily released into the
environ-ment when mined, processed, or used
Mer-cury vapors can be inhaled, and merMer-cury
com-pounds can be ingested or absorbed through
the skin Mercury poisoning has been
recog-nized in native peoples who used cinnabar as a
face pigment, in gold miners who used
mer-cury in processing gold ore, and in hat makers
who used mercury compounds in producing
felt
Inorganic mercury compounds can be
con-verted by bacteria into highly toxic organic
mercury compounds such as methyl mercury
These organic mercury compounds become
concentrated as they move up the food chain
to higher-level organisms such as fish, birds, and hu-mans Because of this the disposal of inorganic mer-cury waste can become a major environmental haz-ard In Japan the release of mercury waste from an industrial plant into the waters of Minamata Bay re-sulted in the deaths of forty-three people during the 1950’s and early 1960’s In 1972, wheat seed treated with methyl mercury fungicide was used by farmers in rural Iraq The wheat was enriched in methyl mer-cury, as was the bread made from the wheat Animals and plants within the area also accumulated high centrations of methyl mercury As a result of this con-tamination, a total of 460 people died from mercury poisoning in 1972
History Mercury has been known since at least the second century b.c.e Chinese alchemists used mercury in fu-tile attempts to transform the base metals into gold Mercury was also used in ancient Egypt Cinnabar, the red ore mineral of mercury, has long been used by ab-original peoples as an important pigment By Roman times the distillation of mercury was known, and a
Chlorine &
caustic soda manufacturing 63%
Electrical &
electronics 16%
Measuring
& control devices 5%
Dental supplies 16%
Source:
Historical Statistics for Mineral and Material Commodities in the United States
U.S Geological Survey, 2005, mercury 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/.
U.S Mercury End-Use Statistics
Trang 10mercury trade between Rome and the rich Spanish
cinnabar mines was well established Beginning with
the Renaissance and the scientific revolution in the
sixteenth and seventeenth centuries, mercury became
important for use in measuring devices such as
ther-mometers and barometers The major modern
indus-trial, medicinal, and agricultural uses of mercury
were developed in the nineteenth and twentieth
cen-turies
The toxicity of mercury compounds has been
known since the early poisoning of cinnabar miners
Later, in the early nineteenth century, the mental
ef-fects that mercury had on felt makers gave birth to the
phrase “mad as a hatter.” The tragic effects of mercury
poisoning were felt in Japan during the 1950’s and
Iraq in 1972, when hundreds died from ingesting
or-ganic mercury compounds
In the United States, the Energy Independence
and Security Act of 2007 will phase out the use of
in-candescent bulbs in federal buildings, to be replaced
by mercury-containing compact fluorescent bulbs
Disposal of the new, energy-saving bulbs will
there-fore require special handling The Mercury Market
Minimization Act of 2008 forbids the sale,
distribu-tion, and export of elemental mercury and bans all
U.S exports as of January 1, 2013
Obtaining Mercury
The primary mercury deposits of the world are found
in Spain, China, central Europe, and Algeria Spain is
estimated to have the greatest reserves, almost 60
per-cent of the world’s total In 2008, world production of
mercury was approximately 950 metric tons Mercury
is also recovered through the recycling of batteries,
dental amalgams, thermostats, fluorescent lamp tubes,
and certain industrial sludges and solutions
Uses of Mercury
In the past, the primary use of mercury in the world
was in the industrial production of chlorine and
caus-tic soda However, beginning in the twenty-first
cen-tury this usage was curtailed significantly, reflecting a
general movement away from mercury usage The
United States has exported refined mercury for the
production of chlorine and caustic soda, fluorescent
lights, and dental amalgam Mercuric sulfate and
mercuric chloride have been used industrially to
pro-duce vinyl chloride, vinyl acetate, and acetaldehyde
Pharmacological uses of mercury compounds include
mercury bichloride and mercurochrome as skin
anti-septics, and mercurous chloride (calomel) as a di-uretic Many of these uses have been curtailed, and a ban on U.S exports was passed by Congress in 2008
Jay R Yett
Further Reading
Adriano, Domy C “Mercury.” In Trace Elements in Ter-restrial Environments: Biogeochemistry, Bioavailability, and Risks of Metals 2d ed New York: Springer, 2001 Eisler, Ronald Mercury Hazards to Living Organisms.
Boca Raton, Fla.: CRC/Taylor & Francis, 2006 Greenwood, N N., and A Earnshaw “Zinc,
Cad-mium, and Mercury.” In Chemistry of the Elements 2d
ed Boston: Butterworth-Heinemann, 1997
Harte, John, et al Toxics A to Z: A Guide to Everyday Pol-lution Hazards Berkeley: University of California
Press, 1991
Hightower, Jane M Diagnosis Mercury: Money, Politics, and Poison Washington, D.C.: Island
Press/Shear-water Books, 2009
Massey, A G “Group 12: Zinc, Cadmium, and
Mer-cury.” In Main Group Chemistry 2d ed New York:
Wiley, 2000
Risher, J F Elemental Mercury and Inorganic Mercury Compounds: Human Health Aspects Geneva,
Switzer-land: World Health Organization, 2003
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 Mercury: Statistics and Information http://minerals.usgs.gov/minerals/pubs/
commodity/mercury U.S Geological Survey Mercury Contamination of Aquatic Ecosystems http://water.usgs.gov/wid/FS_216-95/FS_216-95.html
U.S Geological Survey Mercury in the Environment http://www.usgs.gov/themes/factsheet/146-00 See also: China; Food chain; Hazardous waste dis-posal; Igneous processes, rocks, and mineral deposits; Plate tectonics; Russia; Spain; United States