According to the National Mining Association, gold was first excavated in what is now Eastern Europe around 4000 BC, and it became an international form of currency in Egypt in about 1500 BC. Gold coins appeared around the same time, when the shekel, which originally contained 11.3 grams of gold, circulated widely throughout the Middle East. Within another 500 years, square gold coins were introduced in China, while ancient Greek gold coins appeared in 4th and 3rd centuries BC as staters, tetradrachms, octodrachms, and pentadrachms. Ancient Roman gold coins of the 2nd and 1st centuries BC included the stater, aureus, and binio.
More recently, countries around the world have minted gold coins as currency, usually for larger transactions, although numerous small-denomination coins with trace amounts of gold in them have also been struck. One of the most famous gold coins was the Spanish reale, which was so ubiquitous in early 19th-century America that it was considered legal tender. In the 1850s, the U.S. Mint began producing its own gold coins, some made from ore and nuggets mined during the California Gold Rush of 1949. The largest U.S. gold coins, the $20 double eagles, contained just under a troy ounce of gold by weight. Even heavier were the 5-pound Egyptian coins minted between 1861 and 1957 and the 5-pound British coins struck from 1838 to 1968, both of which had more than an ounce of gold in them.
In the United States, bullion coins have been popular since 1986, when the first American Eagle coins minted under the terms of the Bullion Coin Act of 1985 were released. These coins were minted at the 22-karat standard (.9167 gold) and produced entirely from gold mined in the United States. While American Eagles have a face value, their actual cost depends on their weight (1/10-ounce coins have a face value of $5; 1/4-ounce coins are marked as being worth $10;1/2-ounce coins have a $25 face value; and 1-ounce coins are ostensibly worth $50).
In 2006, the U.S. Mint released its first 24-karat (.9999 gold) gold bullion coin, the American Buffalo, a 1-ounce gold coin created to compete with other 24-karat coins such as the Canadian Maple Leaf. Fractional versions of the American Buffalo were minted in 2008, in the same denominations and weights as American Eagles.
Gold bullion bars are designed for those who want to collect gold in even smaller weights (some as light as 1 gram) than bullion coins. Some of the most popular types of gold bars are Credit Suisse and PAMP, both produced in Switzerland. For heavier bars weighing between 350 and 430 fine troy ounces, everything from their shape (wider on their top surface than their base) to the information stamped into them is carefully regulated. For example, unlike bullion coins, whose weight is guaranteed by the government that issues them, the weight of a heavy gold bar is generally not stamped into the top surface of the bar since it is weighed again before being sold.
Of course you can also collect (or even stockpile) gold in its pure, natural state as gold nuggets, which are usually weathered and pitted due to the erosion of the materials the gold had been in contact with when the nuggets formed. While most gold nuggets on the market are no bigger than your fingernail, some notable nuggets found in Australia have weighed as much as 150 pounds.
As with gold coins, whose numismatic value is often negligible compared to the market value of the metal, gold jewelry and gold wristwatches are often bought and sold just because they are made of gold. This is especially true of off-brand wristwatches and pieces of jewelry whose design dictates a lot of gold, such as a heavy, multichain necklaces or a set of thick, solid-gold bangles.