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Language of Gold

Gold's Purity and Fineness
varied.karats.jpg

© AMNH / Craig Chesek

Karats are a measurement of gold's purity; a karat is 1/24 part, by weight, of the total amount.

Karats are a measurement of gold's purity; a karat is 1/24 part, by weight, of the total amount. Pure gold is described as 24 karats. Because gold is a soft metal, it is often alloyed, or combined, with other metals to make it harder. A metal alloy that is 75 percent gold is measured as 18 karats. Gold content can also be described by its fineness, or gold parts per thousand. Gold containing 25 percent of other metals is said to have a fineness of 750.

varied.color.jpg

© AMNH / Craig Chesek

The color of gold changes when it is alloyed with other metals.

Gold's Color

The color of gold changes when it is alloyed with other metals. Green gold and white gold--which looks like platinum--are used by jewelers. Yellow and pink gold are used for coinage and jewelry.

Wire, Leaf, Branch and Tree

Microscopic crystals of gold take on the cubic shape dictated by the arrangement of its atoms. As one crystal builds upon another, the result is a mass big enough to be visible to the unaided eye, showing eight, twelve or even more faces, or sides. Individual gold cubes are never larger than two centimeters and are extremely rare. However, clusters of parallel growths of gold crystals are much more common, often taking on familiar forms known as wire, leaf, branch or tree. All of these forms use the same crystalline building blocks.

Heavier Than it Looks

Because of its density, a small amount of pure gold can be surprisingly heavy. A one-foot square cube is about the size of one ton of pure gold. A ton of iron would be a cube more than twice this size.

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