Digging through the rubble in my work bench I came across these similar colored pieces. And a vintage glass stone that fits the mount. I like the simple approach..a rivet and a little glue.
The first step is to locate and punch a hole for the rivet. I like to have the back of the piece to look good. so it will be the front of the drop.
After punching the hole for the rivet the next thing is to roll the top of the drop toward the back with bail making pliers
You can see a little additional work needs to be done with a punch to flatten the rivet. Then a little E-6000 to set the stone. I used a 20 inch length of silver chain and darkened it to match the setting by dipping the chain in Swellegant Darkening Patina.
Here is the result...15 minutes , a rivet and a drop of glue and you can have a nice Victorian looking necklace. A materials list includes the setting http://vintagejewelrysupplies.com/4324-filigree-edge-18x13mm-octagon-setting-oxidized-silver-.html And the filigree http://vintagejewelrysupplies.com/4215-the-ultimate-filigree-pendants-oxidized-silver-55mm-.html