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Showing results for tags 'discs'.
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Size like tip of a finger, 34 x 22 x 14 mm. 11 discs, one a bit skewed. Found it approx 30 years ago, been wondering about it ever since. It was found in gravel delivered for a driveway. I have no idea from where. Any suggestions what it is?
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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!