McRocks is not a club and therefore has no membership requirements.
No matter if you are an experienced or newbie rockhound,
we encourage all good people to post messages on McRocks.
The only stupid question here is the one you don't ask!

 
Click the following picture for an illustrated
tutorial on how to post images on the board.

Please don't use IMAGESHACK.US to post images.
Other image hosting internet services are OK.

For tons more rockhounding information:

Welcome to McRocks!
Your hosts, Mike & Chrissy Streeter

Attention Mozilla Firefox Users
Since a login is not required for this message board,
it is totally secure. However, if you're still concerned
about security, you can click on the following link
Click here for McRocks Secure Message Board

 
 
 


Reply
  Author   Comment  
Miles
 #1 
I recently went geode hunting at a local honey hole that was just hit with a lot of rain, and found a 75 lb geode buried in the creek. When I dug it up I realized part of it was already broken off exposing the core, but at it's core is an almost perfect sphere that's white and porous (reminds me of bone). Does anyone know what it could be? Would love to figure out what it really is. Thanks!
BOB HARMAN
 #2 
MILES, 
Without pictures, any ideas what the "core sphere" might be would be mere speculation and guessing.
You actually took the 75 lb geode home?

Since the geode was open in the creek bed, a few guesses might include foreign material, a mud or clay ball,  a corroding calcite crystal, or a quartz snowball in the Iowa geode (google "quartz snowball geodes").    PICTURES PLEASE BOB
Miles
 #3 
Here is a picture of it. The white sphere in the middle has an almost "soapy" texture to it. It's hard to describe. It's definitely not a snowball (I have a few) and I don't believe it's sediment or clay (the quartz lining forms right up against it, like the ball was there before the quartz finished forming). And yes, it was a chore, but I carried the geode out of the creek.

Alright, for whatever reason I can't upload a quality picture because the picture size is too large. I can email you a few picture of it if you'd like, and figure out how to post them on here for others to maybe take a crack at identifying what's in the geode? Anyway, here's a crappy picture just to get the wheels turning.

Attached Images
Click image for larger version - Name: 1506382913330345725420.jpg, Views: 53, Size: 95.13 KB 

Bob Harman
 #4 
MILES,

Like you say, your picture is not very good so I am really still not sure what to make of that. 

Looks like a geode with the central cavity nearly filled with something, perhaps KAOLINITE, a clay mineral, with a sort of soft texture when wet, commonly found in geodes as a coating on other crystals.

Other than that, I have no good ideas....I am really not sure.......I suggest bringing the example to your local club meeting or a local show and showing it, in person, to others.

Sorry I can't be of more help with this.            BOB 
Mike Streeter
 #5 
Miles,

I tend to agree with Bob that your unknown white mineral is kaolinite or perhaps some other similar  clay mineral.  How it ended up in the middle of a geode is not clearly understood and therefore certainly open for debate, but clay minerals, including what appears to be kaolinite, are known to be found in Iowa geodes.

Mike
Sapphire Sue
 #6 
I would third the guess about your white powdery stuff being Kaolinite.  I have found it in geodes in Iowa/Illinois.  It's very white, powdery when scratched, very fine grained.
Miles
 #7 
As far as being powdery, it's not. Actually it's harder to chip than the quartz found in the rest of the geode.
Mike Streeter
 #8 
Miles,

Based on the hardness and opaque white color, the interior of the geode might be composed of chert.  Some geologists contend that Midwest geodes in sedimentary rocks were originally anhydrite nodules that formed in a shallow marine environment and were transformed by complex chemical alteration processes into chalcedony and/or quartz with other minerals later crystalizing into whatever central void space remained available.  It is also believed that anyhdrite can be transformed into chert under just the right geologic conditions.  Since it is known that anyhydrite nodules can often form around a nucleus, including chert, perhaps your geode began as an anydrite nodule with a chert nucleus and was later transformed into a chalcedony/quartz geode with a residual chert center. 

But, the above scenario may just be a BIG stretch on my part and it'd probably take someone with a lot more specific geochemical knowledge than I possess to set us all straight.

Mike
Previous Topic | Next Topic
Print
Reply

Easily create a Forum Website with Website Toolbox.

Return to Message Index Page

 

 

LINKS

US & STATE GEOLOGICAL SURVEYS
MEMORABLE MESSAGE BOARD PICTURES
McROCKS PHOTO ALBUM
FIELD TRIP REPORTS
MINERAL IDENTIFICATION KEY II
MINDAT.ORG
IMAGE POSTING TUTORIAL
ROCK & GEM MAGAZINE
GEMHUNTER'S McROCKHOUND LINKS
McROCKHOUND BIOGRAPHIES