Why is gold measured in Carats?

Hi,
Carat (ct) or Karat (Kt) [in the States and Canada it is Karat] is:
X = 24 * Xg / Xm    
X = the Karat value. 
Xg = the mass of the pure gold.
Xm = the total mass. 
According to that equation 24 Carat (Karat) is 100% pure (in fact 99.99%).  The reaso we use this term is simple convinience: In this way we can talk in simle small numbers: 12, 14, 18, 24.....  rather than saying 75% pure we say 18 karat. 
Best regards,

  4. Why is gold measured in carats?
This stems back to ancient times in the Mediterranean /Middle East, when a carat became used as a measure of the purity of gold alloys (see next Question 5). The purity of gold is now measured also in terms if fineness, i.e parts per thousand. Thus 18 carats is 18/24th of 1000 parts = 750 fineness.

Some sites you maybe interested in exploring are:

The site is: http://www.california-gold-rush-miner.us
 
 
Their museum nuggets are at:
http://www.california-gold-rush-miner.us/australia-gold-nuggets.htm
 
The most expensive gold is called Crystalline gold. Some great photos of it can be viewed at:
http://www.california-gold-rush-miner.us/crystalline-gold-miner.htm
http://california-gold-nuggets-miner.blogspot.com
http://www.brokerforyou.com/brokerforyou/
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http://www.san-diego-dentist.us
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http://www.lasik-surgery-san-diego.info/lasik-eye-surgery-san-diego.htm

gold is usually combined with another metal.  Pure gold is 24kt gold.  So therefore, if you have 10kt gold, you have 10 parts gold, and 14 parts other metal (i.e. copper/nickel).

gold is usually combined with another metal.  Pure gold is 24kt gold.  So therefore, if you have 10kt gold, you have 10 parts gold, and 14 parts other metal (i.e. copper/nickel).