Difference between dark and light
On this ammonite, the darker area is the shell itself, while the much lighter areas are where the outer shell has come away to reveal the chambered shell . This is filled with creamy white calcite. Look carefully in these areas and you can see the suture lines, the wavy patterns made where the chamber walls meet the outside shell. They are only seen here because that outer shell has come away.
The dark shell also has tubeworms growing on its surface. These animals may have colonised the shell when the animal was alive or possibly after it died. There is a way to tell; if the tubeworms are on both sides of the shell, then they may well have attached when the animal was alive. If they are only on one side, then that would suggest that they colonised the upper surface once the animal had died and the shell was lying on the sea bed. This specimen has only been cleaned from one side, so we cannot tell.
Find out more about ammonites on the molluscs pages.