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.

• 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.
• 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).
• Is more malleable than any other metal and can be hammered into foil so thin that it is almost transparent.
• Has a unique ductility property allowing it to be drawn into wire so fine it can barely be seen.
• Is deep yellow in color. Its great reflectivity properties help keep its brightness and color from fading with time.
• 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.
• 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.
• 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.
• Is able to bond with other base metals. This property gives rise to the many different colors available in modern gold alloys.

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

United States Markings	Parts Gold	Gold %	European Markings
24k	24/24	100%	1000 or 999
22k	22/24	91.7%	916 or 917
18k	18/24	75.0%	750
14k	14/24	58.3%	583 or 585
10k	10/24	41.7%	417

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 Avoirdupois weight system, where one pound equals 16 ounces, is used in the United States for most everything except precious metals. The following table summarizes useful weight conversions.

Weight Conversion Table

1 gram (g)	1 pennyweight (dwt)	1 troy ounce (oz t)	1 ounce avoirdupois (oz av)
= 0.643 dwt	= 1.555 g	= 31.103 g	= 28.3495 g
= 0.0032 oz t	= 0.05 oz t	= 20 dwt	= 18.229 dwt
= 0.035 oz av	= 0.055 oz av	= 1.097 oz av	= 0.911 oz t