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Showing results for tags 'paleozoic coral'.
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Hi, everyone, (Just a note that this isn't my specimen or photos -- it was posted earlier today on the Fossil Forum facebook group, and my curiosity over what it is has been bothering me all day. The OP found it along the shore of Delaware Bay years ago, he thinks. Not sure whether he was on the Delaware or NJ side) My guess is that it's a colonial rugose coral like Palaeophyllum, mainly because the longitudinal corallite cross sections in the second photo don't look like heliolitid corallites all packed together, bigger and smaller. But if it is a rugose coral colony, I wondered whether phaceloid colonial rugose corallites can have coenenchymal tissue among them, or if this is something reserved for helolitids. When this photo is enlarged, it looks like there's coral microstructure in the matrix between and inside the corallites. Is it just typical to see this kind of texture in the matrix of rugose colonies? Many thanks-- I hope the question makes a bit of sense! Lisa
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- colonial rugose coral
- delaware bay
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Greetings, My lying eyes are struggling with the unlikely chance that the forms in this rock are biological in origin. This looks like coral to me: I see rough impressions of corallites, polyp anatomy, septa, hexagonal and circular chambers, and signs of stacked chambers where masses are sheared perpendicular to the exterior surfaces. The average diameter of the corallite-like openings is ~.5 cm. Many are smaller. Some are up to 2 cm. Note the manner in which various tilted tubes erode to reveal their lengths and interiors; and the presence of angle-cornered walls that group fields of corallite-like forms (LooksLikeCoral1.jpg). The bed from which these blocks and boulders emerged is sandwiched between crystalline limestone, garnet gneiss, and quartzite. These in turn are closely adjacent to a granitic intrusion. The rock shown here is metamorphic. It feels more dense than quartz, and seems at least as hard as quartz, and reacts very weakly with acid. At a broken edge, its separately fractured crystals reveals the nearly transparent vitreous luster, and the color is proportioned ~95% colorless and ~5% olive green. Examples of the most coherent masses of this rock are seen in LooksLikeCoral1.jpg and LooksLikeCoral2.jpg. A less coherent form of the rock includes a comparatively more easily eroded fibrous mineral that separates the tougher corallite-like layers (see LooksLikeCoral3.jpg). This fibrous mineral is composed of crystals which I believe have the same proportion of colorless and olive green. At the site of the rocks, there is a transition from coherent coral textured masses to less coherent: The fibrous fill increases in volume between ever more deeply curved layers of "remaining" hexagonal nuggets which gradually lose their walls. At one margin of the whole site, the fibrous filler is replaced with marble. And at another, where it approaches the granitic intrusion, there is a transition through stages of melt until the nugget layers are obliterated and mixed into a swirling fine grained mass, finally becoming indistinguishable from quartzite. The site is on privately owned land in the San Ysidro Mountain block of Eastern San Diego County, California. Quite some time ago, this block was determined to go back to the Ordovician, but no physical evidence for this claim has been found. I will test specific gravity, and next week, sections from a sample will be cut and polished for a look inside. I will share the results. In the meantime, it would be interesting to discuss: If you didn't know this was metamorphic rock, would you think these textures and patterns have biological origin? In the unlikely event this is fossil material, do the forms and patterns suggest an ID, and period? If you are forced to speculate that this could indeed be fossil material, what tough mineral/s might have first replaced the biological material so that it could survive the heat, pressure and deformation of mountain building? Just as interesting, can you suggest any non-biological processes that would result in forms and patterns like these? Thanks in advance for replies.
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- metamorphic rock
- paleozoic coral
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