Fossil Petoskey Stone with Tourmaline Sterling Pendant Necklace

The Petoskey stone is ancient fossilized coral found only in the Lake Michigan area.  I've riveted a sterling gastropod or fossilized snail through the stone and backing.  Both sterling silver gastropods feature a small green tourmalines. 

Milled "Jurassic" pattern on the backplate silver. 

Pendant comes with 20 inch square snake chain. 

Thank you for looking!