About Diamond Weights
From Santa Fe Institute Events Wiki
Diamonds are measured in carat weight. one carat weighs 200 milligrams. If a diamond is referred to as four grains, this also means that it is a one carat diamond. The word Carat comes from the word Carob. A carob is a bean that grows on a tree in the Mediterranean. In Ancient times, if a diamond weighed the same as a carob bean, it was one carob, or one carat.
However,in the Far East no Carob trees are found due to the harsh climatic conditions, thus rice was used to measure the weight of a diamond. If a diamond weighed as much as four grains of rice, it was four grains or one carat as we now know it.
Beware when purchasing handcrafted silver jewelleryin which the diamonds are already set or mounted. If more than one diamond is used in a piece, the tag on the jewellery will give the carat total weight - it does not tell you the carat weight of each stone in the piece. You will need to ask the jeweler for the total carat weight of the largest diamond in the piece to truly understand what you are buying.