Fossilised coral formed from corals that lived in the seas around 500 million years ago.
It's officially known as hexagonaria. The finest material comes from around Lake Michigan in the U.S. and from Indonesia.
Fossilised coral from the USA is known as Petoskey Stone.
350 million years ago, Michigan was close to the equator. At that time, a shallow sea covered much of what is now the United States.
Fossilised coral is relatively soft, so must be handled carefully. It exhibits distinctive repeating patterns and can be highly polished.
FLUORITE
