Rainbow-colored ammonite

• Platyceras (Rainbow-colored ammonite)
  Lethbridge, Alberta, Canada
  
  Would you like to know why the ammonite shell in the picture is shining like rainbow?
  Alternate layer of aragonite and conchiolin inside the shell-wall inflect and reflect the light. This causes the shell shine in rainbow color.
  In some countries accessories are made with these Platyceras.