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gold
nugget |
Gold
is a chemical element in the periodic table that has the symbol
Au (L. aurum) and atomic number 79. A soft, shiny, yellow,
heavy, malleable, ductile (trivalent and univalent) transition
metal, gold does not react with most chemicals but is attacked
by chlorine, fluorine and aqua regia. The metal occurs as
nuggets or grains in rocks and in alluvial deposits and is
one of the coinage metals.
Gold was formerly used as a monetary standard for many nations
and is also used in jewelry, dentistry, and in electronics.
Its ISO currency code is XAU.
Gold is a metallic element with a characteristic yellow color,
but can also be black or ruby when finely divided, while colloidal
solutions are intensely colored and often purple. These colors
are the result of gold's plasmon frequency lying in the visible
range, which causes red and yellow light to be reflected and
blue light to be absorbed. It is one of only three metals
which have an actual easily-identifiable color; the other
two are copper, which is red, and caesium, which has a pale
golden color.
It is the most malleable and ductile metal known; a single
gram can be beaten into a sheet of one square meter, or an
ounce into 300 square feet. A soft metal, gold will readily
form alloys with many other metals. This can be done to increase
its strength, or create several exotic colors, sold for instance
in the western United States to the tourist trade as "Black
Hills" gold. Adding copper yields a redder metal, iron
green, aluminium purple, platinum metals white, and natural
bismuth together with silver alloys produce black. Native
gold contains usually eight to ten per cent silver, but often
much more — alloys with a silver content over 20% are
called electrum. As the amount of silver increases, the color
becomes whiter and the specific gravity lower.
Gold is a good conductor of heat and electricity, and is not
affected by air and most reagents. Heat, moisture, oxygen,
and most corrosive agents have very little chemical effect
on gold, making it well-suited for use in coins and jewelry;
conversely, halogens will chemically alter gold, and aqua
regia dissolves it.
Applications for Gold
Pure gold is too soft for ordinary use and is hardened by
alloying with silver, copper, and other metals. Gold and its
many alloys are most often used in jewelry, coinage and as
a standard for monetary exchange in many countries. Because
of its high electrical conductivity and resistance to corrosion
and other desirable combinations of physical and chemical
properties, it also emerged in the late 20th century as an
essential industrial metal.
* It performs critical functions in computers, communications
equipment, spacecraft, jet aircraft engines, and a host of
other products.
* The resistance to oxidation of gold has led to its widespread
use as thin layers electroplated on the surface of electrical
connectors to ensure a good connection.
* It is used in restorative dentistry especially in tooth
restorations such as crowns and bridges.
* Colloidal gold (a gold nanoparticle) is an intensely colored
solution that is currently studied in many labs for medical,
biological and other applications. It is also the form used
as paint on ceramics prior to firing.
* Chlorauric acid is used in photography for toning the silver
image.
* The gold isotope Au-198, (half-life: 2.7 days) is used in
some cancer treatments and for treating other diseases.
* Gold is used as a coating enabling biological material to
be viewed under a scanning electron microscope.
* Many competitions and honors, such as the Olympics and the
Nobel Prize, award a gold medal to the winner (with silver
to the second-place finisher, and bronze to the third.)
* Since it is a good reflector of both infrared and visible
light, it is used for the protective coatings on many artificial
satellites.
* Gold flake is used on and in some gourmet sweets and drinks.
Having no reactivity it adds no taste but is taken as a delicacy.
* White gold (an alloy of gold with platinum, palladium, nickel,
and/or zinc) serves as a substitute for platinum.
* Green gold (a gold/silver alloy) is used in specialized
jewelry while alloys with copper (reddish color) are more
widely used for that purpose.
History of A gold nugget
Gold (Sanskrit jval, Greek crusoV [khrusos], Latin aurum for
"shining dawn", Anglo-Saxon gold, Chinese ? [ji¯n])
has been known and highly valued since prehistoric times.
It may have been the first metal used by humans and was valued
for ornamentation and rituals. Egyptian hieroglyphs from as
early as 2600 BC describe gold, which king Tushratta of the
Mitanni claimed was as "common as dust" in Egypt.
Egypt and Nubia had the resources to make them major gold-producing
areas for much of history. Gold is also mentioned several
times in the Old Testament. The south-east corner of the Black
Sea was famed for its gold. Exploitation is said to date from
the time of Midas, and this gold was important in the establishment
of what is probably the world's earliest coinage in Lydia
between 643 and 630 BC.
The European exploration of the Americas was fueled in no
small part by reports of the gold ornaments displayed in great
profusion by Native American peoples, especially in Central
America, Peru, and Colombia.
Gold has long been considered one of the most precious metals,
and its value has been used as the standard for many currencies
(known as the gold standard) in history. Gold has been used
as a symbol for purity, value, royalty, and particularly roles
that combine these properties (see gold album).
Gold in antiquity was relatively easy to obtain geologically;
however, 75% of all gold ever produced has been extracted
since 1910.[2] It has been estimated that all the gold in
the world that has ever been refined would form a single cube
20 m (66 ft) a side.
The primary goal of the alchemists was to produce gold from
other substances, such as lead — presumably by the interaction
with a mythical substance called the philosopher's stone.
Although they never succeeded in this attempt, the alchemists
promoted an interest in what can be done with substances,
and this laid a foundation for today's chemistry. Their symbol
for gold was the circle with a point at its center (?), which
was also the astrological symbol, the Egyptian hieroglyph
and the ancient Chinese character for the Sun (now ?). For
modern attempts to produce artificial gold, see gold synthesis.
During the 19th century gold rushes occurred whenever large
gold deposits were discovered, including the California, Colorado,
Otago, Australia, Witwatersrand, Black Hills, and Klondike
gold rushes.
Because of its historically high value, much of the gold mined
throughout history is still in circulation in one form or
another.
Value
Gold
Sovereigns with a Krugerrand |
Like
other precious metals, gold is measured by troy weight and
by grams. When it is alloyed with other metals the term carat
or karat is used to indicate the amount of gold present, with
24 carats being pure gold and lower ratings proportionally
less. The purity of a gold bar can also be expressed as a
decimal figure ranging from 0 to 1, known as the millesimal
fineness, such as 0.995.
The price of gold is determined on the open market, but a
procedure known as the Gold Fixing in London, originating
in 1919, provides a twice-daily benchmark figure to the industry.
Historically gold was used to back currency in an economic
system known as the gold standard in which one unit of currency
was equivalent to a certain weight of gold. As part of this
system, governments and central banks attempted to control
the price of gold by setting values at which they would exchange
it for currency. For a long period the United States government
set the price of gold at $20.67 per troy ounce ($664.56/kg)
but in 1934 the price of gold was set at $35.00 per troy ounce
($1125.27/kg). By 1961 it was becoming hard to maintain this
price, and a pool of US and European banks began to act together
to defend the price against market forces.
On March 17, 1968, economic circumstances caused the collapse
of the gold pool, and a two-tiered pricing scheme was established
whereby gold was still used to settle international accounts
at the old $35.00 per troy ounce ($1.13/g) but the price of
gold on the private market was allowed to fluctuate; this
two-tiered pricing system was abandoned in 1975 when the price
of gold was left to find its free-market level. Central banks
still hold historical gold reserves as a reserve asset although
the level has generally been declining. The largest gold depository
in the world is that of the U.S. Federal Reserve Bank, held
at Fort Knox.
Gold in investment portfolios
As a tangible investment gold is sometimes held as part of
a portfolio because over the long term gold has an extensive
history of maintaining its value. It has in the last century
gained ground in relation to fiat currencies owing to inflation.
Gold becomes particularly desirable in times of extremely
weak confidence and during hyperinflation because gold maintains
its value even as fiat money becomes worthless. People who
enjoy investing in gold are known as goldbugs.
Futures contracts based on gold currently trade on various
exchanges around the world. In the US this occurs primarily
on COMEX (Commodity Exchange) which is a subsidiary of the
New York Mercantile Exchange. Speculation about the future
price of gold and other commodities is carried on at COMEX.
Recently, gold-based ETFs like GLD have emerged as a more
convenient investment vehicle.
Occurrence
native
gold |
Due
to its relative chemical inertness gold is usually found as
the native metal or alloy. Occasionally large accumulations
of native gold (also known as nuggets) occur but usually gold
occurs as minute grains. These grains occur between mineral
grain boundries or as inclusions within minerals. Common gold
associations are quartz often as veins and sulfide minerals.
The most common sulfide associations are pyrite, chalcopyrite,
galena, sphalerite, arsenopyrite, stibnite and pyrrhotite.
Rarer mineral associations are petzite, calaverite, sylvanite,
muthmannite, nagyagite and krennerite.
Gold is widely distributed in the Earth's crust at a background
level of 0.03 g/1000 kg (0.03 ppm by weight). Hydrothermal
ore deposits of gold occur in metamorphic rocks and igneous
rocks; alluvial deposits and placer deposits originate from
these sources.
The primary source of gold is usually igneous rocks or surface
concentrations. A deposit usually needs some form of secondary
enrichment to form an economically viable ore deposit: either
chemical or physical processes like erosion or solution or
more generally metamorphism, which concentrates the gold in
sulfide minerals or quartz. There are several primary deposit
types, common ones are termed reef or vein. Primary deposits
can be weathered and eroded, with most of the gold being transported
into stream beds where it congregates with other heavy minerals
to form placer deposits. In all these deposits the gold is
in its native form. Another important ore type is in sedimentary
black shale and limestone deposits containing finely disseminated
gold and other platinum group metals.
See:
• Bullion
• Gold prospecting
• Gold coins
• Gold
as Investment
• Gold
Investing
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This
article is licensed under the GNU
Free Documentation License.
It uses material from the Wikipedia
article "Gold".
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