GMS Field Trip February 2025

GMS Field Trip
Banded Chert/Agate and Oolitic Jasper in Georgia
Saturday, February 16, 2025

The weather in Georgia can certainly be fickle. Only a week before this trip we shed our coats and jackets, but the day of the trip we were walking onions – layered in clothing that still managed to let icy breezes slice through us. But that didn’t stop intrepid GMS members. After Charles gave a quick safety talk, explained the rules of the site, and offered some good intel on where to look, the game was afoot.

Rain the day before, and even that morning, made the site a tad muddy, and that mud relentlessly clung to the rocks, so it required a good eye to see beyond the sticky clay to the wonders beneath. That didn’t slow down our group of determined rockhounds, not even the juniors. Everyone found some pretty pieces.

This site is a geological enigma to us. We know very little about how the fortification agate in the chert formed. We have seen brecciated, i.e., broken and re-cemented rocks, that have fortification agate in the “cement” areas, so whatever process caused the agate seems to have been happening even during major events. There is also very little rhyme or reason to where certain specimens can be found, so Charles describes the site as “tossed salad”. Another tasty morsel in that salad is oolitic (oh-uh-lit-ick) jasper. It is an indication that there was once a marine environment there.

Oolitic jasper consists of ooliths (oh-uh-liths), also called ooids (oh-ids), cemented together. Ooliths are tiny concretions that typically form in shallow marine environments with mild turbulence. It starts with a nucleus that can be anything from a grain of quartz, or biological things like a bit of a shell or shrimp poop. Over time, calcium carbonate precipitates from the water and builds up layer by layer around the nucleus to form an oolith. Ooliths often build up in sediment that eventually becomes oolitic limestone. Silica slowly replaces the calcium carbonate and the rock becomes oolitic jasper. Normally at this location, oolitic jasper can be a bit elusive, but this time it was everywhere, so, being sand people and enjoying tiny things, Olga and I were thrilled.

Speaking of tiny things, Charles and I perused a big pile of small rocks and loaded up on gorgeous little pieces for grab bags right before the trip drew to a close. We had originally scheduled an afternoon trip that had to be cancelled because that site was flooded, so the original end time for the trip was 2:00. Though we could have stayed later, almost everyone was so happy with their goodies that they had already headed home, so we officially ended the trip as originally planned.

It was a such a fun trip and I was amazed at all of the beautiful material coming out. Many thanks to the property owner for allowing us to collect there. Thank you to members who spent such a brisk day together and sharing their finds. Thank you to Kuan Huang, Brian Curtis, Martha Carroll, and Shelley Stubbs for sending pictures. And, of course, thanks to Charles for arranging this trip!

Lori Carter on behalf of Charles Carter
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