GMS Field Trip July 2025

GMS Field Trip
Smaragdite, Corundum, and Garnet Sand in North Carolina
Saturday, July 26, 2025

This was our first field trip with members of the International Sand Collectors Society (ISCS) invited to collect with us. Charles led half of the group to collect smaragdite with pink and red corundum, while I led the other half to collect garnet sand. Despite temperatures in the 90s leading up to the trip, we weren’t hot at all as we collected in wooded areas and in a surprisingly cold creek.

Smaragdite is a variety of actinolite, an amphibole mineral. It gets its green color from chromium. At this location, it often contains small pink to red corundum crystals as well as deep green streaks of zoisite. Members confirmed corundum with long wave UV lights. Charles reported that everyone collected several samples with ease. One of the juniors found a superb piece with both red and blue corundum! Because of the difference in hardness between the smaragdite and the corundum, the material can be tricky to polish, but with a bit of skill and care, it can take a nice polish. I suspect some of the rocks that found new homes that day will end up as some pretty lapidary pieces, while others will be displayed as fine specimens.

When we first collected garnet sand at this location, we wondered why we never found whole garnets or even partial garnets. The sand contains garnet chips that are angular, not rounded, and it also contains a variety of minerals including quartz, mica, and hornblende. If the sand had travelled far from its source, the grains would have become rounded and the sand itself would be more sorted. Based on these observations, we knew to look for source rocks nearby, and we found some! The rocks were identified as biotite gneiss with almandine garnet crystals. The presence of garnet in the rocks indicates high-grade metamorphism during which the garnet formed. When we examined the gneiss, we noticed that the garnet crystals are deformed and fractured. Additional stress during metamorphism most likely caused the deformation and fracturing. As the gneiss weathers, the garnet weathers out in fragments. So, by studying the sand, we learned about the geology of the area!

After Charles brought his group to join the sand group, we all had fun collecting garnet sand and looking for the gneiss that Charles nicknamed “measle rocks”. Jennifer Coor, ISCS member and sedimentologist, explained that we should look on the downstream side of large rocks for garnet sand. Swift water carries garnet-rich sediment downstream. When the water encounters an obstacle, in this case a big rock, the velocity of the water on the downstream side of the obstacle decreases. As the velocity of the water decreases, its ability to hold the sediment in suspension decreases, so the heavy, dense garnet fragments fall out of suspension, while lighter sediment continues downstream. Using this knowledge, juniors found some excellent garnet sand for me! In fact, it is the best sand I have ever collected there!

Thanks to everyone who shared their day with us, we had a great time and I hope they did too. Thank you to Jennifer for teaching us some physics, juniors for helping us, and members who sent photos for this trip report. And, as always, thank you to Charles Carter for arranging another super fun trip!

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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