A Story About Sioux Quartzite
By Pete Carrels
Components comprising Sioux Quartzite were present on Earth’s surface 2.5 billion years ago, when magma rose from the planet’s volatile inner oven. This scorching liquid rock thrust upward through the mantle and crust before erupting into the air and across the land. It was there, freed from the confines of passable vents and fissures, that molten rock transformed into lava. Volcanoes oozed or forcefully expelled gas, ash, and magma. During a time of frequent volcanic eruptions, the world was shaken by gassy explosions and fiery chaos. Subterranean continental plates shifted. Some plates collided. Others slipped farther apart. The force of these geological activities was colossal. The land trembled. Mountains shattered or grew. This process of earth discharging earth continues today, though contemporary ejections seem like rare events.
Varying types of magma are mixtures of different minerals and dissolved gases, and most magma contains silicon dioxide, a primary constituent of quartz. Lava very slowly deteriorates through erosional processes. Solid rock becomes grains of sand.
An enormous inland sea pooled where eastern South Dakota and other parts of the Northern Plains are now. During its lengthy lifespan, that sprawling, fluctuating body of water generated shifting shorelines, and quartz sands carried by waterways or blown by winds accrued at the ever-changing, shallow-watered edges of that sea.
Over millions of years, more and more of those sands settled into that sea, and were transported to downstream locations. Sands at the base of the concentrated deposits were compacted by overlying sediment. That process - the downward force of heavy overburden- squeezed excess liquid from the sand, like pressing down on a water-soaked sponge. The compressed sand grains were then locked together by silica. At this juncture, those sands first delivered by wind and ancient streams had been compacted into sandstone, a loosely grained, sedimentary rock.
About 1.7 billion years ago, that sandstone was subjected to one or more high-pressure tectonic plate events that sank and buried the stone. After weighty pressure lasting five million years, the sandstone was pressed into quartzite. Tinted red, pink, or purple by iron oxide, Sioux Quartzite possesses a texture that is tightly interlocked. In other words, it is a rigid, exceptionally hardened stone. Classified as a bedrock, this particular type of quartzite is visible in few places throughout its range.
In 1867, a scientist named C.A. White visited a quiet hamlet in Dakota Territory named Sioux Falls. A small military post and a handful of settlers huddled there. White, a Massachusetts native, had studied geology at the University of Michigan and medicine at Rush Medical College. He moved his family to Iowa City to open a medical practice but soon realized his real passion was geology and natural history, so he switched careers. It didn’t take long for him to attain recognition and respect. In 1866, the Iowa legislature named him to direct the state’s geological survey. White rose to become one of the nation’s most esteemed scientists, publishing over two hundred papers andbooks, with affifiliations to the U.S. Geological Survey, the National Museum [the original name for the Smithsonian Institution], and the U.S. Department of Agriculture.
White and five companions had earlier departed Sioux City and headed north, following the east side, the Iowa side, of the Big Sioux River. White soon noted the appearance of red boulders “embedded in the deep, rich soil.”
In the northwest corner of Iowa, White encountered “ledges of the red quartzite...” And as the group neared Sioux Falls, they found “quartzite exposed at frequent intervals along the valley.” In Sioux Falls, White studied the cascades of the Big Sioux River and the prominent quartzite formation observable there. In an article published by The American Naturalist, White enthusiastically described the setting. “...we find a magnificent exposure of the same rock extending across the river and causing a series of falls of sixty feet in aggregate height, within the distance of half a mile which for romantic beauty are seldom surpassed.”
White had a special interest in the red stone. “This quartzite,” he wrote, “is of a nearly uniform brick-red color, intensely hard, quite regularly bedded, the bedding surfaces sometimes showing ripple markings as distinct as any to be seen upon the sea-shore of the present day, and which were made in the same manner untold ages ago, when this hard rock was a mass of incolterent sand, the grains of which are even now distinctly visible. In a few localities, it presents the characters of conglomerate, the pebbles being as clearly silicious as the grains of sand.”
White spent several days at the falls before continuing northward to study the rock at Pipestone, the fabled Native American quartzite excavation site. He is now recognized as the first person to use the expression, Sioux Quartzite.
Eighty-two years after White’s scientific mission to Sioux Falls, another geologist, Brewster Baldwin, released a report about Sioux Quartzite. Baldwin, employed by South Dakota’s Geological Survey, was precise in his description of the stone. “The color of the quartzite,” he wrote, “is commonly red or pink, but it can vary over a considerable range. Some exposures are gray or white, with only a faint pinkish cast, and otherwise nearly black. A dark reddish purple is common, and in some places, the fresh rock has an orange tint.” Baldwin also explained the variety of colors: “...the color of the quartzite is due to the presence of thin films of iron oxides coating the grains of quartz.” He noted that iron comprises less than three percent of the rock and, more commonly, one or two percent. Most quartzite surrounding and flooring the cascades is colored a reddish purple. When wet, the rock glistens.
Quarrying the region’s unique, native stone near the falls and in the Sioux Falls area has been commercially pursued since the 1850s. Many of Sioux Falls’ earliest and finest buildings were proudly constructed using Sioux Quartzite. At one point, during the city’s early years, a short-lived and unsuccessful crusade would have required quartzite to be used in all major buildings. For many decades, the emphasis on utilizing local quartzite for structural or ornamental purposes faded, but a welcome renaissance is underway. Especially striking examples of the stone are now commonly used to decorate local architecture.
This story is excerpted from Peter Carrels’ upcoming book, tentatively titled Cascades of the Big Sioux River, A Cultural Geography. He served on FBSR’s board of directors from 2016 to 2021.