Golden Ammonite

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 It is almost certainly a Pyritized Ammonite (specifically from the genus Pleuroceras or Amaltheus). The "gold" you see isn't real gold, but Iron Pyrite (Fool's Gold) that has replaced the original shell material over millions of years.

Why It Is "Golden"

This happened through a rare process called pyritization. When the ammonite died and sank into an environment with very little oxygen (like deep-sea mud), bacteria reacted with iron and sulfur in the water. This created pyrite, which filled in the tiny chambers of the shell before they could be crushed or rot away.

Key Facts

  • Origin: Most of these "Golden Ammonites" come from the Jurassic Coast in the UK (specifically Dorset) or the Franconian Jura in Germany.
  • Age: These date back to the Early Jurassic Period, roughly 180 to 185 million years ago.
  • The Matrix: The dark, crumbly-looking rock it is sitting in is likely oil shale or a dark clay-limestone.
  • Texture: Notice the "ribs" radiating from the center. These are much more prominent and "spiky" than the smooth Moroccan Goniatites you have.

Care Instructions (Important!)

Because these are made of pyrite, they are sensitive to humidity.

  • Pyrite Disease: If they get too damp, the pyrite can react with moisture and oxygen to form sulfuric acid, which causes the fossil to "bloom" with white powder and eventually crumble.
  • Tip: Keep this one in a dry place. Some collectors even store them with a small silica gel packet or give them a light coating of clear archival sealant to keep the "gold" from tarnishing.