One way to check the beads is to wipe them down with alcohol. Then put one between your teeth. Plastic feels different than stone.
Here are some not so good photos of two examples I have that contain similar turquoise beads.
The first contains block Sleeping Beauty beads. There is some slight color variation on the beads and other things that make them not perfect.
The second are natural, Kingman Turquoise beads. A lot more differences in size and colors.
I do not have any necklaces with plastic turquoise bea
ds.
Hope this helps some.