Arizona Jon Posted February 20, 2022 Share Posted February 20, 2022 Found on Arizona mesa top. What’s curious is the shell like structure that I have not seen in the many geodes I’ve found around here. See 3rd and 4th pics for best outer shell view. Any thoughts from the community? Thanks Link to comment Share on other sites More sharing options...
Nanotyrannus35 Posted February 20, 2022 Share Posted February 20, 2022 Just a geode. Pretty nice one though. Enthusiastic Fossil Hunter Link to comment Share on other sites More sharing options...
fossilhunter21 Posted February 20, 2022 Share Posted February 20, 2022 Could it be a geodized bivalve? -@fossilhunter21 Link to comment Share on other sites More sharing options...
FossilNerd Posted February 20, 2022 Share Posted February 20, 2022 I agree. Not an egg. Still, it’s a worthy contender for the “cool rock” shelf. The good thing about science is that it's true whether or not you believe in it. -Neil deGrasse Tyson Everyone you will ever meet knows something you don't. -Bill Nye (The Science Guy) Link to comment Share on other sites More sharing options...
Mark Kmiecik Posted February 20, 2022 Share Posted February 20, 2022 Imagine a shell that thick on an egg. How would the hatchling get out? Jackhammer? That's your first clue that it's not an egg. It's a very interesting geode -- worthy of shelf space! Mark. Fossil hunting is easy -- they don't run away when you shoot at them! Link to comment Share on other sites More sharing options...
DPS Ammonite Posted February 20, 2022 Share Posted February 20, 2022 Welcome to the Forum from Scottsdale. It looks like chalcedony formed as an amygdule in a volcanic rock. Almond shaped cavities in volcanic rocks such as basalt are filled with many secondary minerals including quartz. Note the almond shape of the shell. I bet the mesa is a basalt flow. Where is the mesa? https://en.m.wikipedia.org/wiki/Amygdule 1 My goal is to leave no stone or fossil unturned. See my Arizona Paleontology Guide link The best single resource for Arizona paleontology anywhere. Link to comment Share on other sites More sharing options...
Sjfriend Posted February 20, 2022 Share Posted February 20, 2022 As @DPS Ammonite stated, chalcedony. May be a geode or may be solid. I've found a ton of those near Lake Pleasant and south of I10 west of Tonopah. If the outer shell is solid enough, when cut they can be beautiful when polished. Link to comment Share on other sites More sharing options...
Arizona Jon Posted February 26, 2022 Author Share Posted February 26, 2022 Thanks for the helpful input. Link to comment Share on other sites More sharing options...
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