sponge geode?

[anonaddict]

location: aarhus, denmark
found: loose beach rock
units: metric
date: 01/10/2024

notes: me hit rock with hammer. find shiny.

never found one of these before but ive heard og geodized fossils and based on the shape im guessing it could be a sponge but would like a second opinion

image:

 

 

[Darktooth]

This is not a fossil. It is however obviously crystallized, so is some type of mineral. Not sure if it is agate

[anonaddict]

51 minutes ago, Darktooth said:

This is not a fossil. It is however obviously crystallized, so is some type of mineral. Not sure if it is agate

are you certain? I couldnt think of other reasons for it to be spherical and of a different mineral than the rest of the rock

[Darktooth]

Crystals often form in cavities of the host rock. The cavities are referred to as vugs. Many different minerals form crystals this way and has little to do with the host rock/ matrix. I am still trying to understand why you think it is an agatized sponge? Is it only because of the round shape?

[anonaddict]

9 hours ago, Darktooth said:

Crystals often form in cavities of the host rock. The cavities are referred to as vugs. Many different minerals form crystals this way and has little to do with the host rock/ matrix. I am still trying to understand why you think it is an agatized sponge? Is it only because of the round shape?

because of the sphere shape and the surrounding matrix being rich in tiny fossil fragments. the overall pattern also resembles that of other spherical sponge fossils ive found (usually broken in half with a rough line through or other times whole with a loose piece inside that makes sounds when shaken)

 

im by no means certain of my own id and it wasnt meant to be taken as disagreement with your id. i just like hearing peoples thought process so i understand their reasoning and level of confidence in their assessment so i can learn. for example when i say something is x it's because i'm extremely certain it is accurate, but if I'm adding qualifiers like "i think" or "it might" it's because I really don't know and am only throwing out ideas based on insufficient knowledge. Most people have their own style and it can vary wildly so i just prefer to confirm with people what they base their answers on to avoid confusion.

[Darktooth]

Maybe clearer pics of what you think are fossil bits, because what I see are crystal clusters.

[minnbuckeye]

2 hours ago, anonaddict said:

because of the sphere shape and the surrounding matrix being rich in tiny fossil fragments.

 

Many of my hunting grounds have an abundance of fossils in matrix but also have crystal containing spherical objects scattered through out the formation in the form of vugs and geodes. These objects are strictly geological and I am in agreement with Darktooth that this is likely not a fossil.

[Mahnmut]

Hi,

I cannot say if this is a fossil or not.

In igneous rocks cavities often start as bubbles filled with gases or liquids.

In fossiliferous rocks, which are sedimentary in most cases, cavities can form in different ways. Gas bubbles are also a possibility, fossils are another. Think of the vivianite/anapaite fillled bivalves of Kertsch, agatized corals and calzite filled clams in florida... I have a rudist from France filled with crystals similar in appearance to your find.

So I think if your matrix is rich in unambiguos fossils, the chances that your vugs creation had also something to do with remains of living things are not bad. If its a recognizably preserved fossil is another question.

Look at the details.

Best regards,

J

[anonaddict]

Thanks everyone for sharing your knowledge. I'm a little sad to learn it's not a sponge, but that means it's a vug several times the size of the previous record of mine that i have found and with much nicer crystals and shape. Minor loss for trivia, major win for learning  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(the odds of anyone asking for trivia about my rock collection wasn't massive to begin with)