I am not even sure this is turquoise. It is a very light blue, with spots of colorless, with a dark matrix. Finally, one island of green!
The pictures are much darker. More robin egg blue in real life and maybe a light tint of green in real life.
It tends to shift colors between robin egg blue and into a bit of green. Last one most real to color.
Not marked other than sterling.
I would date it to the 70’s.