The other day, there were some temporary repairs done to my workplace with Bentogrout. Curious about what that was, I asked around and did some research. It’s made of Bentonite, a clay-like mineral that expands with water, so the grout is typically injected into the ground along the exterior foundation wall so it will expand into and seal hairline cracks in the foundation. It also has a South Dakota history…
Bentonite was first identified by Americans stationed at Fort Benton, Montana, a fur-trading post on the Upper Missouri River, where traders used it for packing cracks in horse hoofs and for washing themselves. They called the source sites “soap holes,” where rainwater hit surface deposits of bentonite [Davis and Vacher, 1]. There were reports of Hudson Bay traders using it for washing in Canada before 1873 as well [Davis and Vacher, 1]. It was officially named in the late-nineteenth century by Wyoming state geologist, Wilbur C. Knight, who had initially called in taylorite until realizing it was a duplicate [WSGS Summary Report, 1]. The first commercial shipment of the mineral was made in 1888 by Wyoming quarry owner William Taylor [WSGS Summary Report, 1; Davis and Vacher, 2]. Production continued, but there were jumps in the 1920s and the 1940s as available processing plants and market demand caused growth in the industry.
Bentonite is “any natural material dominantly composed of clay minerals in the smectite group” [WSGS Summary Report, 2]. Sodium bentonite swells more when water is added than Calcium bentonite. The mineral was created when, in the Cretaceous period, deposits of western volcanic ash settled on the shallow seas in our area, settled to the bottom, and were transformed over the millennia from decomposition or the pressure of later sedimentation.
In South Dakota, Bentonite is found naturally in the foothills of the Black Hills, in seams through the Pierre Shale Formation and in seams through the chalk hills along the Missouri River in southern South Dakota. Bentonite is extracted using open pit strip mines, and is processed into a powder for shipment. In continuum from South Dakota, there are major deposits across the border in the northern Black Hills of Wyoming. There also are/have been deposits in North Dakota, Mississippi, Texas, Arizona, California, Canada, Turkey, Greece, Australia, India, Brazil, Germany, Czech Republic, Russia, Ukraine, Italy, Spain, Mexico, and many more.
It became an important industry for the town of Belle Fourche just north of the Black Hills. Will G. Robinson was involved in early extraction [Ellerman 1924, 10]. The Belle Fource Bentonite Products Co. was incorporated in 1923 and owned claims near Belle Fource [Davis and Vacher, 9; Ellerman 1923,16]. The American Colloid Bentonite Company organized in Chicago in 1927 and did the mining and processing of the ore in Middle Creek near Belle Fourche [Davis and Vacher, 9]. In 1940, the Cody Bentonite Co. planned a mill for bentonite processing [Davis and Vacher, 9]. In 1958, a new fourth bentonite plant was built outside town, particularly because of the continued demand for drilling mud and new demands for a binding agent in Minnesota Iron Range taconite production [Hardrock, 1958]. During World War II, the mining of manganese was attempted in the Oacoma zone of the Pierre Formation (remnants can be see from Interstate-90 west of the town of Oacoma), and the seams of bentonite prohibited “wet mining” techniques but there was some home of concurrently harvesting the bentonite [Gries, 190].
Sodium bentonite’s expansive properties can be used in bonding, plasticizing, and suspending agents. Because of it expending into cracks, an important use was for dam construction. The first time that the U.S. Forest Service used bentonite in dam building was as a gel for water extraction during the construction of the Major Lake Dam near Hill City, SD, then began using it as a sealant base for the rock under the dam [Powell, 5-6]. It was used in the Roubaix Dam near Deadwood, Dalton Dam between Rapid City and Deadwood (unsuccessfully), Mitchell Dam near Hill City, Bismarck Dam, and Sheridan Dam [Powell, 5-13]. There were several dams built by the Civilian Conservation Corps in South Dakota constructed with earth fill on a bentonite base that sealed cracks in the rock below the dam. The technique was used outside of South Dakota and created a wider market for South Dakota mines. There are a large amount of uses for bentonite, check out sources below, particularly Davis and Vacher, 1928/1940.
Newton, Henry. “Geological Map of the Black Hills.” New York: Julius Bien, 1879, David Rumsey Historical Map Collection.
Dier, Frank. “A Cowpokes map of Black Hills,” Rapid City SD: Lee Printing Co., 1937. David Rumsey Historical Map Collection. Has a sketch of the American Colloid Co. on the sideline of the map.
Rollins, M.B. et al. Experimental Bentonite Sealing. University of Nevada and USDA, 1963. For reservoirs and canals.
- Belle Fourche History, city website.
- Black Hills Engineer 13(2) (January 1925), 34.
- Clem, Arthur G. and Robert W. Doehler. “Industrial Applications of Bentonite.” Tenth National Conference on Clays and Clay Minerals (c1960), 272-283.
- Davis, C.W. and H.C. Vacher. Bentonite: Its Properties, Mining, Preparation, and Utilization. Bureau of Mines, Department of the Interior. Washington DC: GPO, 1928 .
- Federal Writer’s Project, Works Progress Administration, A South Dakota Guide (Pierre, SD: South Dakota State Historical Society Press,  2005), Tour 13.
- Gries, John Paul. “The Chamberlain, S.D. Manganese Deposit.” Black Hills Engineer 27(3) (February 1942), 189-190.
- Hardrock (yearbook), South Dakota School of Mines, 1948, p3; 1958.
- “Historical Vignette: Fort Randall Dam,” U.S. Army Corps of Engineers website.
- Johnson, Paul R. Soil Survey of Butte County. Soil Conservation Service-USDA and South Dakota Agricultural Experiment Station, August 1976.
- Ladoo, Raymond B. Bentonite, Report to the Bureau of Mines, Department of the Interior, October 1921.
- Lincoln, Francis Church. “The Strategic Minerals of the Black Hills,” Black Hills Engineer 27(3) (February 1942), 177.
- Powell, Ben F. Report on bentonite, its use by Region 2, Forest Service, U.S. Department of Agriculture as an Impediment to Seepage in Small Dam Construction. Denver: USFS, USDA, 1940.
- Sutherland, Wayne M. “Wyoming Bentonite, Summary Report,” Wyoming State Geological Survey (September 2014). Has an illustration of the Cretaceous formation process and map of the deposit regions in Wyoming.
- Ellerman, Otto. Thirty-third Report of the State Mine Inspector for the State of South Dakota, 1923. Thirty-fourth Report, 1924. Series on Google Books.