WI-fossil-guy Posted August 22, 2019 Share Posted August 22, 2019 I have some, what I believe to be, calcareous tufa. I will be posting photos of different specimens over multiple posts and days. All specimens are in partially composed of botryoidal chalcedony. My main question has to with the fact that botryoidal chalcedony is a known pseudomorph in marine fossils. Many of my specimens look like they could be stromatolite-ish or algae-like. Does anyone have knowledge or experience with botryoidal chalcedony and its association with fossils? Can stromatolites or algae sediments become pseudomorphed into botryoidal chalcedony? The calcareous tufa rock that I will post in this message is definitely fossiliferous. You can plainly see three small marine fossils on the bottom-side of the fossil (What might they be?). Two are casts and one is a mold. Generally this rock is "bowl-shaped" overall with a convex top and a concave underside. The rock's top surface is covered with botryoidal chalcedony. There is a smaller amount of botryoidal chalcedony on the underside. Could the botryoidal chalcedony be a psuedomorph fossil? The first photo (#1) shows the rock's upper-side; The second photo (#1B) shows the underside; The third and fourth photos (#1C & 1C-2) are the same fossil object (cast, about 0.5 mm): The fifth and sixth photos (#1D-1 & 1D-2) are the same fossil object (cast, about 1 mm): The seventh and eighth photos (#1E-1 & 1E-2) are the same fossil (mold, about 1.5mm): Link to comment Share on other sites More sharing options...
Brett Breakin' Rocks Posted August 22, 2019 Share Posted August 22, 2019 @ynot because this is above my pay grade. Cheers, Brett Link to comment Share on other sites More sharing options...
caldigger Posted August 22, 2019 Share Posted August 22, 2019 10 minutes ago, Brett Breakin' Rocks said: @ynot because this is above my pay grade. Cheers, Brett What? You're getting paid?!!! My union rep will hear about this! Link to comment Share on other sites More sharing options...
ynot Posted August 22, 2019 Share Posted August 22, 2019 Are You sure that is agate? Could it be calcite? Have You tested the hardness or to see if it fizzes in vinegar? As For Your question about botryoidal agate... It is a form of crystallization of silicate minerals which is developed in voids in rocks when oversaturated water deposits the mineral(s) on the surface of the void. Banding is typical as other minerals are deposited with the agate. This type of agate is found as fossil geodes. Agatized coral from Florida is a good example. I have not seen botryoidal agate in stromatolites as there was no voids in the original biomass, although I have seen agatized stromatolite material. 4 Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
WI-fossil-guy Posted August 22, 2019 Author Share Posted August 22, 2019 YNOT: Thanks for the feedback. The rock does not react in vinegar. That means they are not calcareous, right? Any idea what it could be? Link to comment Share on other sites More sharing options...
ynot Posted August 23, 2019 Share Posted August 23, 2019 If it did not fizz I would say probably agate. Darwin said: " Man sprang from monkeys." Will Rogers said: " Some of them didn't spring far enough." My Fossil collection - My Mineral collection My favorite thread on TFF. Link to comment Share on other sites More sharing options...
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