GMS Field Trip June 2025

GMS Field Trip
Slag, Copper Ore, and Sericite after Staurolite in Tennessee
Saturday, June 21, 2025

The area we visited was mined from the 1840s to the late 1980s. Improper management of waste sulfur caused significant environmental damage that denuded forests, killed most other vegetation, and made the area inhospitable to insects, animals, and humans. By the early 1900s, processes were modified to capture the sulfur instead of releasing it into the air, ironically turning the sulfur from a deadly byproduct to a commercially viable product. Environmental remediation began in the late 1930s and continues to this day. Ore extraction and processing ceased in the late 1980s. The property lay dormant until 2010, when an enterprising company began selling slag and other waste products from the original mining. That company has worked tirelessly to reverse the environmental damage and to help reforest the area.

Originally scheduled for earlier in the year to take advantage of cooler weather, the trip had to be rescheduled a couple of times, so we knew heat would be a major factor when we finally scheduled it for June. With temperatures already climbing early in the day, we arranged our route to maximize time in three locations while ensuring members had time to explore each place safely.

The first location we visited was an enormous slag pile. When copper ore was smelted there decades ago, the copper was separated from iron, sulfur, and other unwanted substances that were collectively discarded as slag. Many people are familiar with glassy slag that consists of mostly quartz, but this slag is not glassy at all because it consists of mostly iron. White micro-crystals of gypsum are “blooming” on the slag, and some are stained green from residual copper. Members enjoyed the odd shapes of the slag as well as vivid colors created by oxidation. Some of the slag exhibits a pattern similar to mud cracks. They probably formed when the slag cooled, the surface cracked, and viscous slag seeped into the cracks. During a prior field trip, we dubbed the pattern “slagon skin”, a portmanteau of dragon and slag. Juniors enjoyed tales of fire-breathing dragons smelting the ore, then rolling around when they got itchy, dropping bits of scaly skin here and there. We moved on to the next location before the pile could become too hot for us.

The second location had two long piles of copper ore to peruse. The piles were moved from elsewhere on the property and placed there by the owner specifically for members to collect. Members found pale blue crusts of gypsum on the rocks as well as raw copper ore. Artifacts from ore processing days were in the piles too, from pieces of equipment to green bricks that got their color from copper leaching from the ore. Many members took large pieces of ore to saw open later.

The last location we visited was a wooded area where the owner dug trenches and set the dirt aside for us to search for pseudomorphs of sericite after staurolite. Sericite is a white mica that forms from staurolite during retrograde metamorphism, i.e., the transition of metamorphic rocks from high temperature and pressure to lower temperature and pressure. The specimens we sought are considered pseudomorphs because the shape of the staurolite was preserved during the process. Many still have unaltered staurolite inside. Specimens are usually found as blades that can measure from a half wide by 1.5 inches long to as large as 2 inches wide by 6 inches long. Although it was fun to look in the trenches, the loose dirt was the best place to look. A vein of sericite in the road yielded several specimens as well as some excellent sericite sand. My favorite piece of the day is a 2-inch wide partial blade where the sericite has replaced all but a few blobs of the staurolite. The shape of the original crystal is beautifully distinct and crisp. Everybody found some good specimens, including the juniors, who also enjoyed playing “the Hulk” with me by crushing chunks of friable sericite rock in our bare hands!

This trip would not be possible without the generosity of the property owner, who is also a GMS member. He goes above and beyond to find and prepare locations for us to visit. The property is a unique geological area with an astounding variety of interesting things, so he is always looking for more for us to collect. A simple thank you is not enough for everything he does for us, so thank you, thank you, thank you!!! Thanks to the members who attended this trip as well. Their excitement and discovery were a joy to us and the owner. And, as always, thank you to Charles for arranging and conducting this trip. His behind-the-scenes work is not always noticeable, but we can all appreciate what he does.

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

Lori Carter on behalf of Charles Carter
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