Gold is a very precious metal. For most cultures, both past and present, it has been of great economic importance. Many nations base the value of their currency on the amount of gold in their reserves (although such gold stashes being “equal” to the amount of paper money is less important now). And gold has historically been the only universally accepted medium of exchange.

What makes gold so valuable?

The most important reason is its rarity, although other characteristics make it valuable, too. For example, pure gold is very softalmost too soft to use in jewelry, unless it is combined with another metal such as silver or copper; it measures about 2.5 to 3 on Mohs’ Scale of hardness. Gold is an excellent conductor of electricity, too, which is why it is so sought after by the electronics industry.

It is heavy-about 19 times the weight of the same amount of water-and is the most malleable and ductile of the metals. Gold can be easily pounded into thin sheets (one ounce can cover an area of about 160 square feet (15 square meters), or drawn into a wire more than 37 miles (60 kilometers) long without breaking. This is why gold leaf church domes and other coverings were once so popular; they allow structures to look lavishly rich while only using a thin coating of gold.

Gold is also almost completely insoluble in nature; in other words, very few liquids will affect it in its natural form. Even oxygen and water do not corrode or rust this metal. (Only a mixture of hydrochloric and nitric acids (aqua regia), and some cyanide solutions will dissolve gold.) Therefore, gold is one of the most inert and stable elements known to humanity.

Are there other types of gold?

Yes, in a way, there are other types of gold, although most have little natural gold in them. For example, white gold, a substitute for platinum, is an alloy of gold with platinum, palladium, nickel, or nickel and zinc. Green gold is usually an alloy of gold with silver. Both are used in the jewelry field. Alloys of gold with copper are a reddish yellow and are used for coinage and jewelry.