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Showing results for tags 'replacement'.
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Hello, I have many crinoid columnals that I collected in gravel (I suppose it was river/creek gravel collected and sold by a "sand and gravel" company) in Illinois many years ago. I have two questions that may be obvious to more seasoned fossil hunters/students. 1) Exactly how did the crinoids actually grow, meaning, how did the stems' diameter expand horizontally in size as time went on, since the stems were mostly composed of hard calcium carbonate/lime. In other words, it seems that once they are "hardened" or "frozen" into a certain size, how can they get bigger? Was there growth tissue on the OUTSIDE of the stem that kept adding on calcium to the inside, like tree trunks creating wood and bark? (I can understand the growth of whorled type seashells, but I can't get this through my head.) 2) Many of the columnal discs/segments I have found are virtually solid silica, some with a glossy almost pearly luster, I suppose would be classified as flint, chert or chalcedony. I assume from what I've read that this is from replacement of the original calcium with silica over a long period of time. This may seem simple-minded or thinking too deeply, but do researchers claim to understand how the silica could actually have "moved" or migrated into the spaces where the calcium used to be? I can't visualize how this would be possible. Like, one molecule at a time gradually moves through solid rock? Does anyone understand why this seems so hard for me to visualize? Or is this believed to occur because the original calcium actually changes it's molecular characteristics without moving? Any input or comments would be greatly appreciated!
Hello everyone, this is my first time posting, I absolutely love this forum. I've decided to register and dive head first. I've recently moved back to Southern Arizona from Florida and I have rekindled my love with rocks, and now fossils, since it would seem I've been finding many of them from all of the ages. Please help me identify this find, it looks carnivorous of some sort, it would be cliche to say it looks like a raptor, but indeed it does. It would be hard for me to believe that this is a fake, since there is also tons of evidence that would point to this being real. (If it is, I'll post more of my finds from the area). I KNOW, I'll get to the point already. I'd just like some real feedback from folks who are more informed and educated in this area than I am. Here it is... and what do you think? Mineralization? Replacement of the softer tissues with minerals? I also have more what look to be different skulls, but some with holes in them and inside you can see bone, which the rock has encased. Found in Southern Arizona. I do apologize for the images being rotated in every direction.
I'm a bit confused with terminology. I always assumed that the fine micro crystalline wood was made through replacement, and therefore the micro structure was very fine, and the specimen was very hard..Picture 1 Where as the coarser fossil wood was formed through silicification and this wood is generally softer and younger than specimens formed by replacement.Picture 2. ( In fact, when looking at the specimen in picture 2 in hand, it is hard to believe this isn't just wood, although it does have pockets with crystals (picture 3). ) Are there obvious features to determine replacement versus silicification, and are older specimens more likely to be formed through replacement, as it seems to be more durable and less likely to degrade?