You want to sell loose diamonds about a carat in total How much approx it is worth?

It all depends on how many diamonds there are to make up 1.0ct, their colour, quality, and cut

I think it would be unfair on our part to tell a price of diamond without even looking at it or seeing the paperwork. Also it would be interesting to see the basics of diamond - Cut (whether it is cut or uncut diamond), color, clarity (is their spark and shine in diamond or not) and Carat value (as mentioned by you- 1 carat here) before taking a call on the price of diamond. Also market price of diamond is one factor which will determine the value you should expect. The current market price for 1 karat diamond is $3,500. But this doesn't mean you will get $3,500. It would be better if you take your diamond to a diamond buyer who will asses it and will tell you the right value. Only check the following thing about the diamond buyer- GIA certified staff, BBB accredited and transparency.