A 0.5 carat with an excellent cut, clarity s12, and colour G costs £1,500. Four things affect the price of a diamond: First, is the weight of a diamond, which is measured in carats. (The bigger the stone, the rarer it is, therefore more expensive).Second, is how perfectly the diamond was cut which determines how well it sparkles! Third, is how clear and colourless the diamond is; diamonds that are tainted are much less valuable than perfectly clear ones. Fourth is clarity which refers to how many imperfections there are in a stone. Diamonds are natural and therefore never perfect and most imperfections that would be carefully noted and graded by a gemmologist using a 10x magnifying loupe are invisible to the naked eye. A 0.5 carat with an excellent cut, clarity s12, and colour G costs £1,500.