Fossil geodes

[Randomguy1]

I found these super cool fossils turned geode today. Any idea what kind of crystals they might be? I was thinking calcite or quartz. Much appreciated. (Edit: Doesn’t react to vinegar, so silica or clear quartz maybe?)

[Randomguy1]

[Tidgy's Dad]

Add a little vinegar to the specimens. 

if it fizzes a little it's probably calcite if not, probably quartz. 

[Randomguy1]

Just now, Tidgy's Dad said:

Add a little vinegar to the specimens. 

if it fizzes a little it's probably calcite if not, probably quartz. 

That sounds like a good idea, some broke off in my pocket after I collected them

[goatinformationist]

Is your specimen a bivalve?  If so then check out my icon (sigil). The crystals in my shells are calcite.  Yours look like silica. Growth faces are different.

Thanks for sharing.

[Randomguy1]

They’re brachs alright. Silica does seem like a good option as the smaller ones seem to resemble the ones on the internet, but the larger ones don’t look exactly right in my mind. I’m not anywhere close to an expert in these things so your answer is better than mine. Fascinating stuff here, thanks for the quick response.

[Ludwigia]

@Randomguy1 Definitely quartz/silicon dioxide . The 2 terms are practically synonymous. Pure silica is a gel which in turn provides the basis for quartz crystals once it combines with oxygen. The crystal on the right in the first photo shows clearly that it belongs to the hexagonal crystal family.

[Randomguy1]

Here’s some real perty ones with what seems to be smoky quartz in the same spot.

[minnbuckeye]

My favorite fossils are geodized. that smoky quartz is beautiful!!

[Randomguy1]

Cool spirifer from same spot 

[Randomguy1]

On 3/13/2019 at 5:52 PM, minnbuckeye said:

My favorite fossils are geodized. that smoky quartz is beautiful!!

Thank you! Those are easily some of my favorite finds