Properties of Gold
Gold is called a "noble" metal (an alchemistic term) because it does not
oxidize under ordinary conditions. Its chemical symbol Au is derived
from the Latin word "aurum." In pure form gold has a metallic luster and
is sun yellow, but mixtures of other metals, such as silver, copper,
nickel, platinum, palladium, tellurium, and iron, with gold create
various color hues ranging from silver-white to green and orange-red.
Pure gold is relatively soft: it has about the hardness of a penny. It is the most malleable and ductile of metals. The specific gravity or density of pure gold is 19.3 compared to 14.0 for mercury and 11.4 for lead.
Impure gold, as it commonly occurs in deposits, has a density of 16 to 18, whereas the associated waste rock (gangue) has a density of about 2.5. The difference in density enables gold to be concentrated by gravity and permits the separation of gold from clay, silt, sand, and gravel by various agitating and collecting devices such as the gold pan, rocker, and sluice box. It’s resistant to corrosion, tarnish and rust.
Pure gold is relatively soft: it has about the hardness of a penny. It is the most malleable and ductile of metals. The specific gravity or density of pure gold is 19.3 compared to 14.0 for mercury and 11.4 for lead.
Impure gold, as it commonly occurs in deposits, has a density of 16 to 18, whereas the associated waste rock (gangue) has a density of about 2.5. The difference in density enables gold to be concentrated by gravity and permits the separation of gold from clay, silt, sand, and gravel by various agitating and collecting devices such as the gold pan, rocker, and sluice box. It’s resistant to corrosion, tarnish and rust.
Gold Color
The color of gold is determined by two factors:
* The type of metal alloys included
* The percentage of each metal alloy
Yellow Gold
Natural gold and color-saturated alloys are what give yellow gold
jewelry its rich shine. The alloys most commonly used, are copper with a
red hue, and silver featuring a green hue. An expert mixture of copper,
silver and pure gold gives this precious metal its signature warmth.
White Gold
A silvery white character is what makes white gold jewelry so
appealing. In order to make the gold white, it is combined with metal
alloys that are white in nature and plated with an extremely hard
element called rhodium. Although strong, rhodium may wear away over
time. Re-plating is a simple process that can be done to restore
whiteness to your jewelry.
Rose Gold
The beautiful pink hue of rose gold jewelry is created by using a
copper alloy. Again, the overall percentages of metal alloys is the same
for rose gold as it is for yellow or white, there is just a different
mixture in what alloys are used.(“Gold Purity, Color, Pricing, and
Care“,http://www.bluenile.com)
Uses of Gold in the Ancient World
Gold was among the first metals to be mined because it commonly
occurs in its native form,that is, not combined with other elements,
because it is beautiful and imperishable, and because exquisite objects
can be made from it. Artisans of ancient civilizations used gold
lavishly in decorating tombs and temples, and gold objects made more
than 5,000 years ago have been found in Egypt. Particularly noteworthy
are the gold items discovered by Howard Carter and Lord Carnarvon in
1922 in the tomb of Tutankhamun. This young pharaoh ruled Egypt in the
14th century B.C.
The graves of nobles at the ancient Citadel of Mycenae near Nauplion, Greece, discovered by Heinrich Schliemann in 1876, yielded a great variety of gold figurines, masks, cups, diadems, and jewelry, plus hundreds of decorated beads and buttons. These elegant works of art were created by skilled craftsmen more than 3,500 years ago.
The graves of nobles at the ancient Citadel of Mycenae near Nauplion, Greece, discovered by Heinrich Schliemann in 1876, yielded a great variety of gold figurines, masks, cups, diadems, and jewelry, plus hundreds of decorated beads and buttons. These elegant works of art were created by skilled craftsmen more than 3,500 years ago.
Ancient Gold Sources
The ancient civilizations appear to have obtained their supplies
of gold from various deposits in the Middle East. Mines in the region
of the Upper Nile near the Red Sea and in the Nubian Desert area
supplied much of the gold used by the Egyptian pharaohs. When these
mines could no longer meet their demands, deposits elsewhere, possibly
in Yemen and southern Africa, were exploited.
Artisans in Mesopotamia and Palestine probably obtained their supplies from Egypt and Arabia.
Artisans in Mesopotamia and Palestine probably obtained their supplies from Egypt and Arabia.
Recent studies of the Mahd adh Dhahab (meaning "Cradle of Gold") mine
in the present Kingdom of Saudi Arabia reveal that gold, silver, and
copper were recovered from this region during the reign of King Solomon
(961-922 B.C.).
The gold in the Aztec and Inca treasuries of Mexico and Peru believed to have come from Colombia, although some undoubtedly was obtained from other sources. The Conquistadores plundered the treasuries of these civilizations during their explorations of the New World, and many gold and silver objects were melted and cast into coins and bars, destroying the priceless artifacts of the Indian culture.
The gold in the Aztec and Inca treasuries of Mexico and Peru believed to have come from Colombia, although some undoubtedly was obtained from other sources. The Conquistadores plundered the treasuries of these civilizations during their explorations of the New World, and many gold and silver objects were melted and cast into coins and bars, destroying the priceless artifacts of the Indian culture.
Early Gold Finds and Production
Gold was produced in the southern Appalachian region as early as 1792
and perhaps as early as 1775 in southern California. The discovery of
gold at Sutter's Mill in California sparked the gold rush of 1849-50,
and hundreds of mining camps sprang to life as new deposits were
discovered. Gold production increased rapidly. Deposits in the Mother
Lode and Grass Valley districts in California and the Comstock Lode in
Nevada were discovered during the 1860's, and the Cripple Creek deposits
in Colorado began to produce gold in 1892. By 1905 the Tonopah and
Goldfield deposits in Nevada and the Alaskan placer deposits had been
discovered, and United States gold production for the first time
exceeded 4 million troy ounces a year: a level maintained until 1917.
During World War I and for some years thereafter, the annual production declined to about 2 million ounces. When the price of gold was raised from $20.67 to $35 an ounce in 1934, production increased rapidly and again exceeded the 4-million-ounce level in 1937. Shortly after the start of World War II, gold mines were closed by the War Production Board and not permitted to reopen until 1945.
From the end of World War II through 1983, domestic mine production of gold did not exceed 2 million ounces annually. Since 1985, annual production has risen by 1 million to 1.5 million ounces every year. By the end of 1989, the cumulative output from deposits in the United States since 1792 reached 363 million ounces.
During World War I and for some years thereafter, the annual production declined to about 2 million ounces. When the price of gold was raised from $20.67 to $35 an ounce in 1934, production increased rapidly and again exceeded the 4-million-ounce level in 1937. Shortly after the start of World War II, gold mines were closed by the War Production Board and not permitted to reopen until 1945.
From the end of World War II through 1983, domestic mine production of gold did not exceed 2 million ounces annually. Since 1985, annual production has risen by 1 million to 1.5 million ounces every year. By the end of 1989, the cumulative output from deposits in the United States since 1792 reached 363 million ounces.
Gold Amalgam
Mercury (quicksilver) has a chemical affinity for gold. When
mercury is added to gold-bearing material, the two metals form an
amalgam. Mercury is later separated from amalgam by retorting.
Extraction of gold and other precious metals from their ores by
treatment with mercury is called amalgamation. Gold dissolves in aqua
regia, a mixture of hydrochloric and nitric acids, and in sodium or
potassium cyanide. The latter solvent is the basis for the cyanide
process that is used to recover gold from low-grade ore. (Harold
Kirkemo, William L. Newman, Roger P. Ashley, “A brief history of gold
uses, prospecting, mining and production”,http://www.geology.com)
Fineness and Karats
Since ancient times the purity of gold has been defined by the term karat, which
is 1/24 part of pure gold by weight. Pure gold is equivalent to 24K.
Gold purity may also be described by its fineness, which is the amount
of pure gold in parts per 1000. For example, a gold ring containing 583
fine gold has 583 parts (58.3%) gold and 417 parts (41.7%) of other base
metals.
The following chart shows the relationship between different international gold markings:
KARAT
|
PARTS IN GOLD
|
GOLD PERCENTAGE
|
FINENESS
|
8K
|
8 in 24
|
33.33%
|
333
|
9K
|
9 in 24
|
37.50%
|
375
|
10K
|
10 in 24
|
41.67%
|
417
|
14K
|
14 in 24
|
58.33%
|
585
|
18K
|
18 in 24
|
75.00%
|
750
|
22K
|
22 in 24
|
91.67%
|
917
|
24K
|
24 in 24
|
99.99%
|
999
|
WEIGHING PRECIOUS METALS
The weight of a piece of gold jewelry is a factor that helps to
determine its value. It is important because it is an indication of the
amount of fine gold in an item of jewelry. Grams (g) and pennyweights
(dwt) are the units of weight most commonly used in weighing gold. Gold
and silver are almost always weighted in the troy system of weights
where one pound troy equals twelve troy ounces and twenty pennyweights
equals one troy ounce. The following table summarizes useful weight
conversions:(”Gold and precious metals information”,
http://www.gottrocks.com)
1 gram (g) = 0.643 dwt = 0.0032 oz t = 0.035 ozav
1 pennyweight (dwt) = 1.555 g = 0.05 oz t = 0.055 ozav
1 troy ounce (oz t) = 31.103 g = 20 dwt = 1.097 ozav
1 ounce avoirdupois (ozav) = 28.3495 g = 18.229 dwt = 0.911 oz t
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