Why is Karat Used for Gold?

Have you ever had a post-workout protein bar that looked like it was covered in decadent chocolate, only to bite into it and it tasted like paper?  That was probably carob on the outside, not chocolate.  And although a healthier alternative, it is just not the same.  Well, while carob may not be rich in flavor, it is certainly rich in history.  The carob tree is an evergreen native to the Mediterranean and Middle East.  The seeds were used by African and Middle Eastern traders for weighing gold and other goods because of their uniform weight and size.  Kirât is the Arabic word for seed.

In Roman times, a pure gold coin was designated as weighing 24 kirât (karats) or 24 seeds.  This evolved into the standard designation that pure gold has 24 parts and we refer to pure gold as 24 karat gold.  Eventually the weight for one kirât or seed was standardized to 0.20 grams, hence a 1 carat diamond weights one seed, or 0.20 grams.  The term karat is conventionally used only for gold, although carat is interchangeable between diamonds and gold.  We use karat vs carat mostly by convention in the United States.  Gold is expressed in karats and diamonds in carats, although now you know they originally sprouted from the same seed.