Gold Coins

A Gold coin is a coin made mostly or entirely of gold. In modern times, most gold coins are intended either to be sold to collectors, or to be used as bullion coins, coins whose nominal value is irrelevant and which serve primarily as a method of investing in gold.
Gold has been used as money for many reasons. It is fungible with a low spread between the prices to buy and sell. Gold is also easily transportable, as it has a high value to weight ratio, compared to other commodities, such as silver. Gold can be divided into smaller units, without destroying its value, it can also be melted into ingots, and re-coined. The density of gold is higher than most other metals, making it difficult to pass counterfeits. Gold is extremely unreactive.

Collector Coins
Many factors determine the value of a gold coin, such as its rarity, age, condition and the number originally minted. Gold coins coveted by collectors include the Aureus, Solidus and Spur Ryal.
In july 2002, a very rare $20 1933 Double Eagle Gold Coin sold for a record $7,590,020 at Sotheby's making it by far the most valuable coin ever sold to date. In early 1933, more than 445,000 Double Eagle Coins were struck by the U.S Mint but most of these were surrendered and melted sown following Executive order 6102. Only a few coins survived.
In 2007 the Royal Canadian Mint produced a 100KG gold coin with a face value of $1,000,000, though the gold content was worth over $2 million at the time. It measures 50 centi metres in diameter and is 3 centimetres thinck. It was intended as a one off to promote a new line of Canadian Gold Maple Leaf  coins, but after several interested buyers came forward the mint announced it would manufacture them as ordered and sell them for between $2.5 million and $3 million. As of may 3, 2007, there were five order.
Austria had previously produced a 37 centi metres diameter 31 Kg philharmonic gold coin with a face value of 100,000. Euro.
On October 4,2007,David Albanese stated that a $10, 1804 dated eagle coin was sold to an anonymous private collector for $5 million.
In 2012 the Royal Canadian Mint produced the world first gold coin with a 0.11-0.14ct diamond. The Queen's Diamond Jubilee coin has been crafted in 99.999% pure gold with a face value of $300.


Fineness of Gold Coins:
Coins are usually mode of an alloy as other metals are mixed into the coin to make it more durable. Fineness is actual gold content in a coin or bat and expressed as a per mil or thousandths. For example, a gold ingot identified as being .999 fine will be 999/1000 pure gold, with the other 1/1000 being an alloy.
Karat weight is a traditional fraction based system used to denote the fineness of gold with one Karat being equal 1/24 part of pure gold in an alloy. With the precision of modern assaying techniques, however the fineness of gold ingots  and bullion is more likely to appear as a decimal measurement. In this system, pure gold would be denoted as 1.000 fine. However, since absolutely pure gold is very soft and therefore not suitable for coinage or ingots, it is generally accepted worldwide that anything above .999 fine qualifies as 24K.
Below is a Karat weight to fineness conversion chart
Correlation between karat and fineness

• 24 Karats = .999 fine or above
• 23 Karats = .958 fine
• 22 Karats = .917 fine
• 21 Karats = .875 fine
• 20 Karats = .833 fine
• 18 Karats = .750 fine
• 16 Karats = .667 fine
• 14 Karats = .583 fine
• 10 Karats = .417 fine

The fineness is often converted to a percent, as well. If a gold coin has a fineness of  .900, that is 90.0% pure gold. if a gold coin has a fineness of .850, then the gold coin is 85.0% pure.