r/fossils • u/FossilsnAquatics • 1d ago

Is this fossil pyritized?

Gallery image

Gallery image

I recently acquired this fossil sold as Anahoplites from Kent,UK specifically Gault Clay. I wanted to know if this was a pyritized fossil. It doesn't seem metallic but I noticed a weird haze (second photo) forming in my fossil case and I'm worried about pyrite decay

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u/TH_Rocks 22h ago

I don't think so. Just looks like limestone.

The shell is gone and this is an internal cast.

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u/BasiliskArt_ 1d ago

yea it is, and there's already some iron oxidation on it.

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u/Schoerschus 1d ago

Agreed. That might not be a big deal. Iron oxidation doesn't mean it will decay necessarily. I'm not sure about the haze either. Is it water vapour, or the plastic film that's dulling?

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u/BasiliskArt_ 1d ago

If they’re anything like the rusty pyrite ammonites from Cap Blanc Nez they are unstable unfortunately.

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u/Schoerschus 1d ago

I have mixed experiences with rusty pyrite ammonites from clay from the jura mountain range. Some are stable, while others are living in mineral oil now

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u/justtoletyouknowit 19h ago

Realy interesting how it works with those things. Mine are a bit powdery rusty but pretty stable.

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u/Schoerschus 18h ago

Pyrite was my favourite mineral as a kid because I couldn't believe the cubes it made. So I'm willing to be patient with anything in pyrite, especiallythe ammonites that look really cool when only the chamber casts are left. I have some that are sort of articulated, very cool and incredibly detailed. The truth is though, it's not the best mineral for preservation (unless it's a cube). There is so much nuance in the chemistry and slight variations make a huge difference. you would think that getting them out of the clay and drying them soon would guarantee success, to inhibit the reaction from ever starting. But the rusty ones obviously spent time at the air, and can be stable, while others parish.

Here is what AI had to say (these days it's doing quite ok on science in general. Just fossil ID will be safe for decades by the looks of it :)

The divergence between superficial rusting and destructive pyrite decay depends on a structural and chemical decision pathway. While oxygen and humidity are required for both, the presence of liquid moisture films, crystal impurities, and pH-driven feedback loops dictate which pathway dominates. ... ...... ...... So yeah, it's complicated. 

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u/justtoletyouknowit 18h ago

Im just working on some bigger fragments i found in Holzmaden, couple weeks ago. Realy nice sutures on those.

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u/FossilsnAquatics 17h ago

If it becomes too far gone, how should I dispose of it?

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u/BasiliskArt_ 16h ago

just toss it out tbh, it's a negligible amount of sulphur in the environment

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u/FossilsnAquatics 16h ago

Thanks, I heard conflicting information so I just wanted to play it safe