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I have a rock with a lot of fossils in it - What should I do?


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BillRigg

Hey all! So I found what appeared to be a large geode, but upon further investigation turned out to have 5 or 6 fossils imprints! They seem to be seashells, scallop-like so possibly bivalves or brachiopods. I'll attach the pre-cleaning pictures below, then some more later after I rinse it and dry it off.

My big question is: since this thing definitely has fossils (I can see at least two are half buried in the stone matrix) and is very likely a geode (it's heavy, has dimples, and I can see shiny facets in a few of the dimples), what should be next step be?

I wanted to crack it open along the big crack down the side of it, thinking it would expose a crystal core. But I see these fossil imprints and I don't want to risk breaking them in cracking open the rock.

So then, since I've only found some amateur fossil finds (mostly in riverbeds and on beaches), what should I do next? 

Seems to me the likely responses are crack it open and hope for the best (immediate gut-reaction of anxiety for fear of smashing the imprints too), or try to securely remove or break off the fossil fragments for a bigger cracking later, or to airblast portions of it, or to send it to a museum? I'm not certain and I definitely don't want to damage the thing in the meantime as the sheer age of it has made me quite fond of it.

 

Any advice or recommendations would be welcome!!

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Ludwigia

That does not appear to be a geode, but rather solid sedimentary stone. If you have an air scribe, you could work your way into the rock to the shells, which are probably bivalves. If not, then you could give it a whack to see what's inside. If there are any decent fossils in there, then they usually sheer off at the shell.

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BillRigg

Hey Ludwigia, thank you! Do you think it's not a geode? I only thought so because of the weight, the dimple holes in it, and the fact that some of the holes are lined with crystal facets.

 

That said, thanks for the feedback! About the fossils - that makes sense! There seem to be some "soft fossils" or imprints of fossils on the outside of the rock (see the first picture), should I not care so much about these? I feel like they're gonna be toast if I smash the thing.

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BillRigg

Also, not to double-post but I've seen some mention of freezing it overnight to try and get it to crack more gently and naturally. Thoughts?

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Thomas.Dodson

As Ludwigia mentioned this is not a geode but solid sedimentary rock. Some crystal replacement of sediment is normal.

26 minutes ago, BillRigg said:

Should I not care so much about these? I feel like they're gonna be toast if I smash the thing.

The answer to this depends on what you want out of this fossil. The imprints on the exterior are not significant or identifiable but if you like it the way they are there's nothing wrong with leaving it as is.

 

11 minutes ago, BillRigg said:

Also, not to double-post but I've seen some mention of freezing it overnight to try and get it to crack more gently and naturally. Thoughts?

This works best with particular concretions of certain sedimentary rock that have very well defined planes of weakness and are susceptible to damage from hammering. I doubt you'd get the results you want with this rock by freezing. I don't think this rock absorbs enough water to cause expansion and stress.

 

I'm guessing you don't have an air scribe so I'd give this some controlled whacks with a cold chisel. To start I'd line up the chisel with existing cracks (see picture) that might form along planes of weakness from more significant fossils and hammer this way, increasing force gradually until the rock splits. With the crack on the right I'd angle the chisel on the plane of the existing fossil to try and expose the rest of it.

 

Some possibly obvious notes on safety: Don't use a wood chisel. Claw hammers and specialty hammers aren't really made for metal on metal impact but I'm guilty of using my rock hammers for short term and minor chiseling. It's always a good idea to wear safety glasses anyway.

 

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Tidgy's Dad

Could be fragments of rhynchonellid brachiopods.................

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