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Hilton Jr., B. 1995. Hidden treasures: Rocks and minerals of the South Carolina Piedmont. South Carolina Wildlife 42(2):34-36.

(Note: The draft below was submitted to South Carolina Wildlife magazine; the article that actually appeared in print may have been edited.)

To many observers, the main geological attributes of South Carolina's Piedmont are "red clay and rolling hills," and it is these two features that are often most remembered by out-of-state visitors to the Upcountry. Even though hills and clay are obvious components of our Piedmont landscape, the earth beneath our feet contains a wealth of "hidden treasures" that delight anyone who takes time to explore the geology of the region.

Piedmont red clay and rolling hills are both signs of past grandeur, when the region was marked by vast mountains as tall as modern-day Himalayas. Over millennia, those once towering "Piedmont Mountains" were nearly leveled by geologic change and incessant cycles of rain and wind, freezing and thawing. Gentle hills blanketed with layers of red clay are the result.

Today, the Piedmont, which cuts a broad northeast/southwest swath across nearly a third of the state, has few spectacular geological features. The highest terrain is less than 1,500 feet above sea level. There are scattered monadnocks--tall, isolated hills that are the lasting remains of ancient mountain chains--but for the most part the Piedmont is gently undulating landscape with many rivers and streams that continue to slowly wear away at native soil and rock. If you scrape through the topsoil almost anywhere in the Piedmont, you're bound to find thick, moist red clay within a few inches of the surface. Like the hills, this clay has its own story to tell, and it also disguises a variety of rocks and minerals that lie hidden below.

The predominant underlying bedrock of the Piedmont is metamorphic--slates, schists, and gneisses, with occasional granite intrusions--all the result of intense pressure and heat from subterranean movement. Some of the red clay that covers these Piedmont rocks was deposited over time as flowing water swept sediment down from higher altitudes, but most of it formed from beneath as "weathering" changed the nature of the subsoil through mechanical and chemical processes.

The color of red clay comes from the ferrous nature of the bedrock--not usually enough iron to be mined and processed into steel, but plenty to tint the soil a deep rusty red. Although there were small Piedmont iron mines at Blacksburg and at Nanny's Mountain near Bethel during the Revolutionary and Civil Wars, today the red clay itself is a resource of much greater value than our sparse iron reserves. For example, there were no active South Carolina iron mines in 1987, but that year clay pits in the Piedmont yielded more than $38 million in raw materials.

Along the Catawba and Broad Rivers, particularly rich deposits of red clay are mined and turned into high quality brick for homes and commercial buildings. Brick making has been so significant in fueling the development of the Upper Piedmont region that some historians consider construction of the local brickyard as a pivotal event in the establishment of early Carolina settlements; the presence of clay sometimes dictated where a town began. (Historical note: Prior to construction of local brick plants, structures were sometimes built with ballast bricks from European ships carried by barge and wagon from Charleston to northerly Piedmont counties.)

Clay of another type was even more significant to the original inhabitants of the Piedmont. For generations, Catawba Indians in Lancaster and York Counties have dug a unique gray, silky clay from isolated deposits along the river that bears the tribe's name. Superior clay from these sites is still used to make traditional Catawba pottery that is highly collectible and that has become an economic mainstay for many local artisans.

The Catawbas, as Native Americans, were among the first people to harvest several other Piedmont mineral resources. They had favorite spots for collecting raw quartz they turned into tools and works of art--arrowheads, spear points, knives, and scrapers--and rare in-state soapstone deposits held sacred significance for other tribes. Soapstone was prized by Indians because it was easily worked into utilitarian bowls or ceremonial pipes and took on a mystical sheen when polished. Associated with soapstone veins at Pacolet Mills and in Cherokee County are pockets of corundum, an aluminum oxide that forms rubies and sapphires that--then as now--were admired for their gemstone qualities.

Historical accounts indicate that Indians also knew of a rare yellow metal that in about 1820 caught the attention of the "white man." Prospectors spread the word that gold was in our Piedmont hills, and by 1827 there was a full-fledged South Carolina gold rush that pre-dated by two decades the more famous one in California. First documented gold production in the Palmetto State occurred in 1829, and over the next 113 continuous years of mining the state produced 318,825 ounces of gold. In that span, Lancaster County's Haile Gold Mine was the largest gold producer in the eastern United States, and in later years was also a source for "mineralite," a substance used in insulators and paint. Since about 1975 there has been additional in-state exploration for gold; currently, the only producer in the eastern U.S. is a mine at Ridgeway, a facility that makes South Carolina the sixth most productive gold state in the nation.

Most places in the Piedmont, all that glitters really ISN'T gold, but there are a number of sparkly minerals that catch the eye. One of the most common is mica, a transparent planar crystal that reflects sunlight and has a variety of uses. Historically, large sheets of particularly transparent mica substituted for glass panes, and the mineral is still used to make viewing windows for experimental high-temperature furnaces.

Several prosperous sites centered around Enoree in Spartanburg and Laurens Counties take advantage of another of mica's properties. At these facilities, mica-laden rock heated in special containers expands and breaks into lumps of a fluffy product known to gardeners as "vermiculite." Most vermiculite is marketed as a water-holding additive to potting soil, while the rest is used as lightweight aggregate in concrete or as a substitute for asbestos insulation.

A mining operation of a different type occurred from 1947 to 1970 at Henry's Knob in northern York County. Over 23 years, this towering Piedmont landmark shrunk more than 100 feet in height as bulldozers stripped away layer after layer of rock to reveal the world's largest deposit of kyanite. According to Butch Maybin, Chief of Mineral Resources for the South Carolina Department of Natural Resources' Geological Survey, kyanite is a crystalline form of aluminum silicon oxide used in the manufacture of high-quality ceramic bricks. As the mother rock was crushed and washed, insoluble kyanite crystals--called "blue daggers" by the miners--floated to the surface of the water and were skimmed off, with the tailings flowing away to form huge sterile deltas down the slope of Henry's Knob.

When kyanite mining stopped in 1970, much of the mountain was a desolate wasteland--including a seven-acre, highly acidic pond that is still stained a deep blood red. Local ecologists doubted the site would ever recover--Henry's Knob Group of the Sierra Club even took the mountain's name as a rallying cry for action--but after two decades of re-planting and the spreading of lime to de-acidify the soil, the locale is showing signs of new life. Even so, it will be hundreds--perhaps thousands--of years before Henry's Knob returns to a more natural condition.

Because stricter state and federal mining laws have been enacted, the kind of operation that caused disastrous results at Henry's Knob could never occur again in South Carolina, and mining companies are now required to restore an area once it has been depleted of product. With such wise regulation, amateurs and commercial operators alike will still have access to minerals and gemstones of the Piedmont, and our valuable earthen resources will continue to benefit the state and its citizens in many ways.

And who know knows? Further exploration by some sharp-eyed weekend rockhound wandering our rolling hills might one day turn up a new "hidden treasure" beneath the red clay of South Carolina's Piedmont region.

Miscellaneous "Hidden Treasures" of the Piedmont:
  • The dominant mineral product in the Piedmont is crushed and dimension stone, with 1987 production listed at $78 million.
  • There are deposits of amethyst at Due West and Jonesville.
  • Marble quarried at Gaffney was used as a flux in Revolutionary-era iron and steel-making operations. (Nearby Blacksburg was also known as "Iron City" for its metal works.)
  • Lead mines at Gaffney and copper mines at Abbeville produced ore during the Civil War period.
  • White, dense barite from a mine at Kings Creek was used as a weighting agent in flour and sugar.
  • High-quality quartz mined at Laurens is used in electronics manufacture.

POSTSCRIPT (adapted from Clemson University's "South Carolina Studies"):

Henry's Knob Kyanite Mine (Southeast of Kings Mountain)

Henry's Knob was once the highest point in York County. Composed of hard quartzite rock, the mountain was much more resistant to erosion than the surrounding rock, which was composed of a metamorphosed mud rock called schist. However, quartzite rock also contained an aluminum-rich mineral known as kyanite and in 1935 enterprising miners began carving up pieces of the mountain to extract and process this valuable mineral. Production increased greatly after 1948 to the extent that, for the most of the 1960's, South Carolina was the second largest producer of kyanite in the entire country. By the time mining operations ceased in 1966 the top of the knob had been completely removed and its elevation was lowered by more than 300 feet(?). The main excavation pit cut almost all the way through the hill from one side to the other.

Kyanite is a hard, bluish mineral with a very high melting point. It is used in the manufacture of ceramic items such as spark plugs that must withstand not only high temperatures but sudden changes in temperature as well. Although the mineral itself is non-toxic, the refining process uses a highly acidic liquid that was collected in open pits and left to seep into the groundwater system. Leftover rock waste, or tailings, was likewise dumped over large areas of the hillside. At the time of the mine's closing, close to 2,000 acres of land had been turned into a dead zone with high levels of contamination all around.

When the Henry's Knob kyanite mining operation became unprofitable, operators simply left the area with no clean-up and no attempt at reclamation. In most mine closings the owners will either allow the open pit to fill with water and become a lake or they fill the pit with trash and tailings and turn it into a landfill. In the case of Henry's Knob, various buildings and parts of buildings were left standing, concrete and other foundation structures were left in place and unburied, and rock waste from screening ponds was left covering most of the site perimeter. Some of this material still washes into nearby streams every time it rains.

Fortunately, after decades of neglect, nature has begun to reclaim portions of Henry's Knob. Trees were planted and other vegetation is slowly starting to cover some tailing areas, but it will be a very long time before this corner of York County can blend in harmoniously with its surroundings.

Bill Hilton Jr. is a science education consultant, writer, naturalist, and Macintosh computer enthusiast who lives in York, South Carolina.

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