If you don't have hundreds of dollars to drop on a high-end necklace, take a look at Aimee's tutorial at Swellmayde.
Aimee mixed an assortment of small clear rhinestones with a few large green gems. She used clear vinyl as backing and attached the rhinestone clusters to a chunky chain.
To make a similar necklace, you will need five large gems in settings and about 60 smaller clear rhinestones in various shapes. You will also need chunky chain, 12 jump rings, clear vinyl, jewelry glue and a lobster end clasp.
See the full tutorial at Swellmayde.