In gemstones or Nine Gemstones means “ Navratana” Carat system is used
Carat is also used in gold jewellery for the purity of gold. e.g. 22 c or 23 c where as the standard of pure gold is 24 c which is the purest form of gold.
Here carat is a weight measurement system i.e. as under
Cara = 1/5th of gram
i.e. 0.200 mg.
e.g. 5 carat = 1.00 gram.
So the greater the weight of the diamond, the rarer it is, hence the demand of it and its value increases greatly with its size.