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Gold is one of the
most precious metals in the world. It is present in the
rivers, seas, and the earth’s
crust and trace amounts are present in plants and animals. It
is, however, difficult and expensive to extract. In modern
mining operations approximately 3 tons of ore are needed to
extract one ounce of gold. The many desirable qualities found
in gold, along with its scarcity, have made it the most
popular metal for use in jewelry today.
Properties of
Gold
Gold in its pure
state:
- Has a melting point of
1945 degrees Farenheit (1063 degrees Celsius). When
alloyed (chemically combined) with other base metals
the melting temperature of the resulting alloy is
changed. 18K yellow gold has a melting point of 1675
degrees Farenheit and 14K yellow gold has a melting
point of about 1550 degrees Farenheit.
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- Has a specific gravity
of 19.33. It is relatively heavy compared to most
metals, such as silver (SG 10.7) or iron (SG 7.8). A
notable exception is platinum (SG 21.4).
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- Is more malleable than
any other metal and can be hammered into foil so thin
that it is almost transparent.
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- Has a unique ductility
property allowing it to be drawn into wire so fine it
can barely be seen.
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- Is deep yellow in
color. Its great reflectivity properties help keep its
brightness and color from fading with time.
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- Will not rust, tarnish
or corrode. Gold jewelry recovered from ancient
Egyptian tombs is in the same state as when placed
there over 4000 years ago.
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- Is softer than most
other metals. On the Mohs scale of hardness (which is
a measure of a gemstone or mineral’s resistance to
scratching), gold has a hardness value of 2 to 2.5.
Diamond has a value of 10. Pure gold may easily be
scratched. Fortunately, gold becomes harder when
alloyed with other base metals.
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- Is relatively scarce
and therefore expensive. It is estimated that only
125,000 tons of gold have been mined the world over
since the beginning of time.
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- Is able to bond with
other base metals. This property gives rise to the
many different colors available in modern gold alloys.
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Fineness
(Karat Value)
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.
Federal Trade Commission
rules require that all jewelry items sold in the United
States as gold shall be described by "a correct
designation of the karat fineness of the alloy." No
jewelry item less than 10K may be sold in the United
States as gold jewelry.
The following table lists
the relationship between different international gold
markings.
Fineness
of Gold Karats |
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