This piece features a Boulder Opal Doublet focal gem stone wrapped in a 22K gold bezel with a 10K gold back sheet.  There is a little faceted round emerald, in 18K gold, attached to the opal bezel and all suspended by an open link 18K gold chain.

Side note from artist (me:) I think this opal looks like a landscape.  Just for fun, I did an image with it as a background .... see image #3.

This piece is one of a kind and handmade in Soho, NYC.

Necklace Length is 16-1/2". 
The opal itself is 1/2' long x 7/8" wide x 1/8" deep. 
With the emerald the total drop length is 7/8".