This necklace is composed of a single chain and sea glass. with a longer chain and sea glass added to give it a “stack”. This is a lovely way of giving the appearance of stacked necklaces without getting them all tangled at the back. 
The shortest chain in this necklace double stack is about 17”, so this sits more like a choker necklace. If you would like it to be slightly longer, please select to add the extension chain, which will make the shortest chain 18”. 
Some people believe as glass is man-made, sea glass doesn't have any spiritual healing properties. However, I like to think about the transformation that sea glass has gone through as a result of the natural elements. Sea glass starts off as an (arguably ugly) shard of man-made glass that enters the sea. After years and years of living in the salty, wavy ocean, the sharp edges are naturally worn away to create something smooth and beautiful. It's incredible to think about the journey this piece of glass has been on.