Emerald and aquamarine are both the same mineral. The only thing that distinguished them is their color. So a hybrid color is possible, though less common. Its usually called "Green Beryl". Its value will really depend on its aesthetics, but it won't be worth as much as a nice emerald. And the name "Aquald" is just a marketing ploy of his - it's a made up name that he is using to try to make it more exotic. Is there any way you can get him to give you a picture and post it?