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Mineralogical ClassificationAgatized Snail - Mineral or Fossil? Or both?

28th Sep 2015 19:36 UTCBrian Greenstone

I bought this in Denver, and it's one of our favorite finds of the show. However, I didn't get a whole lot of information about it other than where it was from, so I'm hoping someone here can help me out. Here's a movie of it: https://www.youtube.com/watch?v=Ynxn98Lp0ao

First, would you classify this as a fossil or a mineral specimen, or both?

Second, any idea how old this might be?

Thanks,

-Brian

28th Sep 2015 19:45 UTCJamison K. Brizendine 🌟 Expert

I would define them as both !

Ohio was well known for producing Spirifer fossils that had been psuedomorphed into pyrite. These were from a quarry in Sylvania, Lucas County. I rarely see these at shows anymore...

One of my fellow Cleveland club members, told me a very funny story that they did a theme case of minerals to show at one of the Cincinnati Shows. The theme of the case was minerals that were also fossils. To make a long story short, they won the award for having one of the best fossil cases. I don't remember the details of the story, but it was either Terry or Marie Huizing who was in shock when they announced that the Mineralogical Society of Cleveland was the winner.

28th Sep 2015 19:48 UTCAlfredo Petrov Manager

That's sort of like asking whether you eat your food with a fork or with metal. Both, of course. It's a fossil, and it's a mineral. It fits well into either type of collection. (Lovely piece, by the way!)

28th Sep 2015 19:52 UTCBrian Greenstone

Thanks! I guess my confusion is whether it's technically a fossil because of the way the shell was replaced by agate. For example, take a steinkern. It's just hardened mud from the inside of a gastropod, but not actually the fossil of the gastropod itself, so I'm not entirely sure what to classify that as either. I'm not really sure if these agate snails form in the same way as ordinary fossils, or if it's a different method that results in more of a cast of the original snail, thus not actually a fossil. Does that make any sense?

-Brian

28th Sep 2015 20:13 UTCKelly Nash 🌟 Expert

I think your definition of fossil might be too restrictive. Fossils are just remains or traces of animals or plants that have been preserved (per the AGI Dictionary of Geological Terms). Thus a steinkern is a fossil, as are other casts, molds, tracks, impressions or other traces of ancient life.

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