I’m not sure what that stone is, but it isn’t turquoise. Maybe some others on the site will have some ideas.
A photo of the entire necklace and back of stone setting might help with ID.
By the limited photo, I’m guessing green opal (Madagascar) which is a hydrated silicate mineraloid.
I haven’t seen this stone before. I agree with others that full photos of the necklace, front & back, could be helpful. Taking a lead from @StevesTrail, I looked at non-turquoise stones online and came across (Green) Tremolite cabs. They look similar to this stone, imo. One site indicated that the cabs are from Pakistan. Just another avenue to explore…
To me it looks somewhat like Green Jasper with milky quartz from Brazil.
@fernwood I took a look at green jasper online. What’s being referred to as Spotted Jasper looks really close to this stone in appearance. You may be onto something here.
this “HENNA JASPER” stuff keeps showing up in my image searches