This image displays several pieces and sections of chain coral, more officially known as Halysites. They are a form of extinct coral that lived in the Paleozoic era, roughly 540 to 250 million years ago.
Photo by Lucy Gridley
The description states:
CHAIN CORAL
Silurian coral, chain coral, Halysites. Found in both peninsulas of Michigan. Interesting jewelry is made from cross section and longitudinal cuts of this petrified coral.
–Silurian refers to the time period that the coral likely lived, approximately 440-420 million years ago. The card is dated 1962.