Link Posted July 20, 2009 Share Posted July 20, 2009 What characteristics of a concretion would indicate that it's got a fossil in it? What shape, size, rock type, location, etc. should I look for? Link to comment Share on other sites More sharing options...
Auspex Posted July 20, 2009 Share Posted July 20, 2009 What characteristics of a concretion would indicate that it's got a fossil in it? What shape, size, rock type, location, etc. should I look for? Concretions are generally dense and exceedingly fine-grained. They tend to form around an organic nucleus, but whether or not any trace is preserved is a bit of a snarge-shoot. "There has been an alarming increase in the number of things I know nothing about." - Ashleigh Ellwood Brilliant “Try to learn something about everything and everything about something.” - Thomas Henry Huxley >Paleontology is an evolving science. >May your wonders never cease! Link to comment Share on other sites More sharing options...
Terry Dactyll Posted July 20, 2009 Share Posted July 20, 2009 Is a concretion the same as what I call a nodule?.... I have found both fine and more coarse grained nodules, usually depending on the sediments that the nodule has formed in.... apparently, quite quickly after burial, the nodule gradually grows outwards from the nucleus, which may be a small grain of rock but is very often the remains of a dead organism. Gases from the decay of the organism may react with minerals in the surrounding sediments which creates and forms a localised, denser more stable sediment, long enough to allow an impression or preservation of the creature...In such cases, the organism is quickly encased in a protective rock ‘shell’. When the rock is later buried at depth and subjected to crushing pressure and destructive temperature, the fossil within the nodule is protected and survives. Fossils in nodules are so well protected, that they usually even retain their three-dimensional structure. Concretions or nodules can often be fossil shape dictated as the fossil is often the central growth point as the nucleus.... Heres a 'Part formed Nodule' I photographed a couple of years ago.... where chemical/mineral conditions were not quite right to fully complete the process.... Note how the sediments have changed somewhat around the shape of the frond, but not quite formed 'siderite' to complete the process..... and the shape of the ferm tip fragment has dictated the shape of the nodule.... Cheers Steve... And Welcome if your a New Member... Link to comment Share on other sites More sharing options...
Link Posted July 20, 2009 Author Share Posted July 20, 2009 According to 'kipedia: "There is an important distinction to draw between concretions and nodules. Concretions [are] formed from mineral precipitation around some kind of nucleus while a nodule is a replacement body." So I guess what you are referring to are actually concretions... Link to comment Share on other sites More sharing options...
Terry Dactyll Posted July 20, 2009 Share Posted July 20, 2009 Link... Thanks for the definition.....the decay of the organism (the nucleus) initiates minerals to change the immediate surrounding rock which form the nodule...so should i stop calling nodules , nodules, and call them concretions? Cheers Steve... And Welcome if your a New Member... Link to comment Share on other sites More sharing options...
jeepinthemud Posted July 20, 2009 Share Posted July 20, 2009 so THATS how that type of lizard does it... it make the rocks around it harden, so it is protected inside its shell! (they can live decades in that rock house) "To do is to be." -Socrates "People are Stupid." -Wizard's First Rule "Happiness is a warm Jeep." -Auspex Link to comment Share on other sites More sharing options...
micropterus101 Posted July 21, 2009 Share Posted July 21, 2009 Concretions vary greatly in productivity when you go by shape and size. Each locale is different. Some place you dont bother with round ones other places the round ones are the only productive ones. Most crab guys look for oblong depressed concretions but are missung out if they ignore round or irregular concs from some localities. Bottom line is ya just gotta get out there and bust open thousands of rocks before you get that sixth sense and good search image thing going for you. fossil crabs website Link to comment Share on other sites More sharing options...
Recommended Posts