What is 1 gram diamond worth?

Lacking a quality definition as to the stone's clarity, colour or cut, the answer can only be -- it depends on how much someone will pay you for it.

For the price of a latte, you may be able to buy a bag of industrial diamonds weighing many grams. However, a gemstone of this weight -- five carats, could bring up to US$481,520 if you were Blue Nile and the colour was "D" and the clarity Internally Flawless.