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Polish Diamond
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Diamond in the rough
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The unit of weight used for diamonds is the metric carat, which is 0.2 grams. Weight is the most objective of the Four Cs since loose diamonds can be weighed directly and precisely on a balance. Mounted diamonds cannot, but their weights can be calculated from careful measurements.
Carat is often express as ct. This carat is different from karat which is a measure of gold purity. To learn more about karat, please click here.
Most precious gemstones are also using ct. as a unit of weight except for pearl (momme for lot and diameter in mm for individual) and few other organic gemstones. A cocktail ring with a single sapphire centre and 20 diamonds set around it labeling 1.50ctw does not mean the centre sapphire is 1.50ct. Any item other than solitaire is often presented by carat total weight (ctw, cwt or total ct.). Some stores might give you a combined total weight of different gemstones in one single item even though it is against industry ethical practice. Other stores would provide individual weight or total weight of one or more stones of same species. Make sure to ask what is included in the total weight when purchasing jewellery.