Opal halo surrounding green topazpendant on 20" sterling silver

opal pendant with green topaz on 20" chain. platinum plated sterling silver genuine opal. brand new with tag. plenty of fire in the opal. marked and tested 925 signed sts. my cheap diamond tester says those are diamonds but disclosure they may be diamonds or possibly sapphire but I wasn't told what they are so not selling as such but letting you know they might be. def moves the tester.