No one can tell by a picture, especially with stones non-descript as Aqua and Prasiolite.
Aqua is a very cheap stone until you get into very blue quality. It could be either one.
The neckless was probably mass produced with thousands of carats used. When you buy that much of any commercial quality stone you are paying pennies on the dollar on the carat.
Much of this is made in India. Very cheaply. Not saying it is not pretty, but the cost is very low to manufacture.