GMS Field Trip September 2025

GMS Field Trip
Lace Agate/Chert in Georgia
Sunday, September 14, 2025

For the second year in a row, GMS hosted the Southeast Federation of Mineralogical Societies (SFMS) annual meeting, including a field trip for SFMS delegates. Everyone who attended the trip found some excellent lace agate/chert, and had a chance to have Charles face polish pieces on the spot or even try their hand at polishing!

Having collected there for many years, I can say that the lace banded agate/chert from this location is as enigmatic as ever with its speleothem-like appearance – as though it just came out of a cave! Layers of large crystals intertwined with layers of fine banding add to the geological mystique. As rocks from deeper down are revealed, we have noticed that they are denser and less prone to fractures, making them highly prized for lapidary use. The colors have changed over the years too, from pale pink and light gray to dark pink and deep chocolate red. The contrast between colors has changed from barely visible to stunningly distinct layers.

One of my favorite rocks to find there is made of ooliths (oh-uh-liths). An oolith is a sand-sized (up to 2 mm) mostly spherical concretion that is formed layer by layer from a precipitated mineral, typically calcium carbonate. Ooliths usually form in a shallow marine environment where calcium carbonate is plentiful and gentle movement of water allows it to precipitate and accrete around a nucleus of quartz, shell fragment, or even tiny poop. As ooliths become less mobile, minerals in the water can fill in between them and cement the ooliths together. The resulting sedimentary rock is called oolite (oh-uh-light) and is described as being oolitic (oh-uh-lit-ick). Oolitic limestone retains the calcium carbonate, but at this location, it has been replaced by silica. The result is a rock that exhibits the beautiful concentric layers of each oolith, and can be polished nicely as well. From a geologic sense, it is important to note the presence of oolitic rocks because they indicate that a shallow marine environment existed there at some point.

Charles had permission to bring a cabbing unit to the site, so he brought one of the first prototypes he built from extruded aluminum and 3D-printed parts. People stopped by with a rock that he would face polish a bit to bring out the beauty of the stone. He also stepped aside so people could polish rocks themselves. For some, it was their first time using a cabbing unit.

It was a beautiful day to collect beautiful rocks! Many thanks to the property owners for allowing us to collect there and use the cabbing machine. Thank you to everyone who attended the trip and showed us their favorite finds. And, of course, thank you to Charles for setting up and running the trip, and for polishing stones for everyone!

Note: Specific location information is not included in this report to maintain the privacy of the property.

Lori Carter on behalf of Charles Carter
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