GMS Field Trip

GMS Field Trip
Geology Hike and Various Minerals in Georgia
Saturday, May 4, 2019

The Georgia Mineral Society sponsored a field trip to a local nature preserve to hike through its historic quarry and examine the Lithonia gneiss that was quarried there. During the week before the trip the weather reports for the weekend were uniformly stormy, and since the quarry surfaces are mostly bare rock with some organic veneer, park rangers warned us against going into the quarry during or soon after heavy rain because the walking surfaces became slick and dangerous. Because of this, the field trip was called off by email on Thursday before the weekend.

The drenching rain turned out to be spotty thunderstorms. On Saturday morning I drove to the park to evaluate the trail and catch any people who showed up. The trails were dry, the quarry was dry and the rangers said that the area had not received significant rain at all. One family, Cameron Clines and his daughter Cristina had not gotten the cancellation notice. One of the park rangers joined us and the four of us walked the quarry, keeping an eye out for any storms.

We found dozens of small shallow catch-pools that allow a habitat for several rare plant species and many animal species. The ranger pointed out flora and fauna to us, we saw frogs and salamanders, tadpoles and snakes and several species of dragonfly.

We also noted the texture of the gneiss, its large and small-scale folding and granularity. In several places we found interesting minerals in the phenocrysts that collected in some of the folds, with quartz, mica and tourmaline. Along with broken fragments of quarried rock we found several “feather” nails, rusty iron spikes a few inches long, which were pounded into cracks to help break out stone blocks. We found several places where the gneiss appeared to be in the process of spalling, breaking away from the surface underneath. We also found several abandoned ten-foot blocks of granite from other quarries, which the ranger said had been shipped to this site for processing at one point.

The path took us across the quarry to an abandoned supervisor’s building then down to a lake. Coming back along the lake trail was sheltered under trees the whole way and a relief from the sun. We made it back to the parking lot before it started raining.

Because of the exposure on the quarry surface, this trip will not be held again during the summer heat, but may be offered in the autumn.

Tom Faller, Trip Lead
On behalf of Charles Carter, GMS Field Trip Chair
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