How much is a 10K carat of diamond worth?

Whatever you have to sell is worth whatever someone will pay you for it.

If you have a single stone of this carat weight, take it to a certified gemologist so that you can most fully understand its clarity, colour and the cut. This will help you establish a market value for it.

If these are loose, gem-quality diamonds, you can have them documented individually.

If you have a bag of industrial diamonds weighing ten carats, which are valued differently from gem-quality diamonds, the value will be determined in pounds not carats.