This is the magnetic "frame" for the Evolution Collection in a Satin Finish Sterling Silver, by Petra Azar. The chain length is adjustable. It can be worn alone or adorned with several inserts reflecting individual Birthstones or your favorite color stones.
Image two shows the elegant insert in white sapphire and polished sterling silver. If you look at the top of the third image you see hearts along the chain. These hearts are movable to adjust the length of the Evolution 1 pendant chain. Ingenious!
The insert is sold separately for $75 (link)
The third image shows the pendant and insert together. The fourth image was a bit difficult to photograph (for a novice like me) since the magnets are so strong, the component pieces had to be far enough apart so they didn't magnetically merge!