Flint(?) Concretion

Discussion in 'Cephalopod Fossils' started by Terri, Mar 27, 2012.

  1. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    This concretion is about 3cm. in diameter, it really looks like flint to me, I'm sure I could be wrong and I think I may be be seeing conchoidial fractures. The concretion formed around a nucleus that appears to have some structure, wether it's a fossil or not I don't know. :roll: I really expected the outside of concretion to sizzle, but it didn't, neither did the black flinty looking stuff nor did the nucleus. Any insight appreciated! :smile:
     

    Attached Files:

  2. DWhatley

    DWhatley Cthulhu Staff Member Moderator

    Joined:
    Sep 4, 2006
    Messages:
    19,085
    Likes Received:
    1,131
    Location:
    Gainesville, GA USA
    Is that as round as it looks in the picture? I have seen lots of rounded rock but not rocks that are round so it really stands out. Could be something man shaped as a weapon?
     
  3. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    Yes, it's my understanding that concretions can be perfectly round. I've had this for years and just enjoyed it but my curiousity got the better of me and I decided to crack it. I wasn't expecting to see the flintlike material or such a cool nucleus (possibly fossil?). Hopefully Kevin will clear things up. 8-)
     
  4. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

    Joined:
    Nov 19, 2002
    Messages:
    2,391
    Likes Received:
    94
    Location:
    somewhere under the desert sky
    Chert Nodule, commonly round, sometimes a fossil, sometimes not. I don't see anything there that looks like it could be a fossil. :sad:
     
  5. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    :oops: I went round and round (pun intended) :heee: on wether to call this a concretion or a nodule. What I read was that concretions always form around a nucleus, and when I searched nodules they were mostly oddly shaped formations. So I'm incorrect? :confused:
     
  6. DWhatley

    DWhatley Cthulhu Staff Member Moderator

    Joined:
    Sep 4, 2006
    Messages:
    19,085
    Likes Received:
    1,131
    Location:
    Gainesville, GA USA
    Kevin,
    Can you explain the difference in what you would see between a geode and a nodule. I read the Wickipedia distinction but it was not clear how you would visually determine if the core was coated or formed as part of the rock (correct this undersanding of the differences if my paraphrase does not properly match the concept :oops:). Include in your tutoring how you would determine that this is not a geode please :sagrin:
     
    Terri likes this.
  7. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    I'm finding what seems to be a lot of contradictory information on nodule vs, concretion. I thought I had it penned down to concretion, but I will gladly concede to Kevins superior knowledge. :razz:
     
  8. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

    Joined:
    Nov 19, 2002
    Messages:
    2,391
    Likes Received:
    94
    Location:
    somewhere under the desert sky
    A geode is hollow with crystals growing inside. A geode is a nodule that is hollow. :heee:


    The best explanation is found HERE
    Also see Siderite and Phosphate concretions/nodules.

    To me, generally, concretions are large and soft(er) and nodules are small and hard. :sly:
     
    tonmo likes this.
  9. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    So, chert nodule instead of flint concretion, thanks Kevin! :smile:
     
  10. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

    Joined:
    Nov 19, 2002
    Messages:
    2,391
    Likes Received:
    94
    Location:
    somewhere under the desert sky
    Chert and flint are the same thing, aren't they?
     
  11. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    Well, after reading the great link you supplied, of course you would be correct, chemically speaking. Technically, I should have called it chert. I read this article and based the decision to call the material flint on color and texture instead of chemical makeup. http://www.quartzpage.de/flint.html

    So, the differences in cryptocrystalline quartz, chalcedony, chert and flint would be crystal size and specific gravity and are nearly identical in chemical makeup to that of pure quartz. 8-)

    Thanks again Kevin!
     
    Architeuthoceras likes this.
  12. DWhatley

    DWhatley Cthulhu Staff Member Moderator

    Joined:
    Sep 4, 2006
    Messages:
    19,085
    Likes Received:
    1,131
    Location:
    Gainesville, GA USA
    :sagrin: so does that make it a geode if the cryptocrystalline quartz, chalcedony, chert, flint had larger crystals and a hole in the center? :roll:
     
  13. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    I believe, basically, you would be right. But I bet we could make it a whole lot more complicated than that if we wanted to.:heee:
     
  14. DWhatley

    DWhatley Cthulhu Staff Member Moderator

    Joined:
    Sep 4, 2006
    Messages:
    19,085
    Likes Received:
    1,131
    Location:
    Gainesville, GA USA
    At least it is just a little more sophisticated than calling it a round thingy :grin:
     
  15. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
  16. Architeuthoceras

    Architeuthoceras Architeuthis Staff Member Moderator

    Joined:
    Nov 19, 2002
    Messages:
    2,391
    Likes Received:
    94
    Location:
    somewhere under the desert sky
    Round Thingys or Geodes... Maybe if we said geodes are purty and chert nodules aren't (unless they contain fossils)...

    :heee:
     
    DWhatley and Terri like this.
  17. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    My geodes aren't as "purty" :mrgreen: as the ones in Kevins link, here's one I picked up in Kentucky on a bank of Grant Lake. I'm not sure but I think the crystals are calcite?
     

    Attached Files:

  18. Solius

    Solius Blue Ring Registered

    Joined:
    Feb 13, 2011
    Messages:
    30
    Likes Received:
    17
    Hi all. First post.

    I was taught that chert, flint, jasper, ect are colloquial terms for the mineral chalcedony which is composed of micro-crystalline SiO₂. Too, geodes have chalcedony rinds or they are just nodules. I have seen geodes with several generations of xl formation that led to total filling of the cavity.

    Things might have changed. It has been 25 years since mineralogy and I haven't really kept up.
     
    Terri and Architeuthoceras like this.
  19. Terri

    Terri Sepia elegans Registered

    Joined:
    Dec 20, 2009
    Messages:
    960
    Likes Received:
    85
    :welcome: Solius! Having had a mineralogy course you have a better grasp than I do on this topic. According to this link Moganite has recently been added to the mix that is chalcedony...http://www.mindat.org/min-960.html...:hmm: From what I've read and am attempting to grasp, everything you stated I believe is correct.
     
  20. DWhatley

    DWhatley Cthulhu Staff Member Moderator

    Joined:
    Sep 4, 2006
    Messages:
    19,085
    Likes Received:
    1,131
    Location:
    Gainesville, GA USA
    ... and I am just trying to translate the concepts into something simple enough to follow and relate :oops:
     

Share This Page