![]() Pure elemental gold is 24 karats, while 18-karat gold is 75 percent pure gold, 14-karat gold is 58.5 percent pure gold, and 10-karat gold is 41.7 percent pure gold.Gold metal flakes may be eaten in foods or drinks, although it is a common allergen for some. Although gold is a heavy, dense metal, it is generally considered nontoxic.Very thin sheets of gold may appear greenish blue because gold strongly reflects red and yellow. ![]() A sheet of gold can be made thin enough to be transparent. ![]() A single ounce of gold can be beaten into a 300-square-foot sheet. Malleability is a measure of how easily a material can be hammered into thin sheets.Gold threads can even be used in embroidery. A single ounce of gold (about 28 grams) can be stretched into a gold thread 5 miles (8 kilometers) long. The element symbol for gold-Au-comes from the old Latin name for gold, aurum, which means "shining dawn" or "glow of sunrise." The word gold comes from the Germanic languages, originating from the Proto-Germanic gulþ and Proto-Indo-European ghel, meaning "yellow/green." The pure element has been known since ancient times.Nearly all the gold on Earth came from meteorites that bombarded the planet over 200 million years after it formed.Gold is the only metal that is yellow or "golden." Other metals may develop a yellowish color, but only after they have oxidized or reacted with other chemicals.Chlorauric acid (HAuCl 4) is used to preserve photographs by replacing the silver atoms present in an image. Gold sodium thiosulfate (AuNa 3O 6S 4) is used as a treatment for arthritis. Gold coated mirrors can be used to make telescopes that are sensitive to infrared light.Ī radioactive isotope of gold, gold-198, is used for treating cancer. Gold is also a good reflector of infrared radiation and can be used to help shield spacecraft and skyscrapers from the sun's heat. Gold is a good conductor of heat and electricity and does not tarnish when it is exposed to the air, so it can be used to make electrical connectors and printed circuit boards. One karat is equal to one part in twenty-four, so an 18 karat gold ring contains 18 parts pure gold and 6 parts alloy material. The amount of gold in an alloy is measured with a unit called a karat. Gold alloys are used to make jewelry, decorative items, dental fillings and coins. Pure gold is soft and is usually alloyed with other metals, such as silver, copper, platinum or palladium, to increase its strength. One sheet of gold leaf can be as thin as 0.000127 millimeters, or about 400 times thinner than a human hair. Thin sheets of gold, known as gold leaf, are primarily used in arts and crafts for gilding. A single ounce of gold can be beaten into a sheet measuring roughly 5 meters on a side. Gold is the most malleable and ductile of all known metals. It has been estimated that all of the gold that has currently been refined could be placed in a cube measuring 20 meters on a side. There is roughly 1 milligram of gold dissolved in every ton of seawater, although extracting it currently costs more than the gold is worth. Gold is sometimes found free in nature but it is usually found in conjunction with silver, quartz (SiO 2), calcite (CaCO 3), lead, tellurium, zinc or copper. An attractive and highly valued metal, gold has been known for at least 5500 years.
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