Written by: Emily Moffat, Regulatory Approvals Coordinator, Archaeological Survey of Alberta
Stone tools were central to life in pre-contact North America and the rocks that they were made of were highly valued. The archaeological record throughout vast regions of North America, including much of Alberta, contains Knife River Flint (KRF), one of the most significant and intriguing tool stones used before the arrival of Europeans. KRF gets its name from the Knife River, a tributary of the Missouri River that flows through the United States Midwest and Southeast Regions.
In an era of limited human mobility compared to modern times, KRF was regularly transported hundreds of kilometres from its source in North Dakota, where it was quarried for thousands of years. A relatively small geographical region contains the majority of quarry pits and this location is the hub of KRF’s widespread distribution.
Over the course of 13,000 years, KRF was shaped into projectile points, tools, and some unusual eccentric forms. Its translucent, coffee-brown colouration, ability to flake predictably, and stay sharp were desirable qualities. Some speculate that the bison-hunting peoples of the past may have even attributed spiritual properties to the stone. Whatever the reasons, KRF was considered significantly more valuable than other local materials, so great effort was invested in its procurement.
Dunn and Mercer Counties of North Dakota were the most intensively quarried regions, and evidence of those activities is still found on the landscape today. Pre-contact quarry pits appear as pock marks on LiDAR imagery, a remote sensing technique that removes surface vegetation. The primary source area is about 200 hectares and contains 29 pit complexes, each with up to 75 individual pits per hectare. On average these pits are 6 metres in diameter and 1 metre deep, with the largest reaching 20 metres in diameter and 2 metres deep. The pits visible on imagery represent the most recent quarrying activities but many were excavated two or three times prior, illustrating the high demand for KRF.
KRF first formed when low-grade coal, called lignite, was turned to stone by silica (SiO2, e.g. quartz) mineralization. These original rock formations, thought to be about 50-30 million years old, were eroded by glaciers and water, resulting in secondary deposits of loose pebbles and cobbles. KRF could therefore be pried from the ground fairly easily as opposed to chipped from a rock face or collected as river cobbles like some other lithic materials. Tools typical to the period, such as fire-hardened digging sticks and bison scapula hoes and shovels, would have been used to unearth KRF.
KRF quarrying activities were one of the first preserved instances of natural resource extraction in the region, and efforts were well organized. People may have camped at or near the quarry sites for several days or intermittently over weeks to dig for KRF. At the quarry pits, high quality cobbles were often flaked by hammer stones into smaller, more manageable cores that were either made into tools at nearby workshops or transported elsewhere for trade. Discarded flakes from this process still remain at the quarry sites today. In total, an estimated 12.5 million kilograms of KRF were acquired, from which 640 million KRF tools/cores were thought to have been made. About 160 million of these were exported beyond the primary source area, covering a 4.8 million square kilometre extent. KRF is therefore considered one of the most productive and widely circulated lithic raw materials in North and South America.
KRF materials were brought to Alberta through trading and long distance travel. A relatively high number of archaeological sites in Alberta contain KRF (243 sites), the furthest being about 1500 km from Dunn County, North Dakota. The abundance of KRF in Alberta’s archaeological record has fluctuated over time, but its presence spans the nearly 13,000 year human occupation of the province. The spread of KRF throughout pre-contact times hints at trade and settlement patterns as people adapted to the changing landscapes of Alberta’s past, which saw the creation and disappearance of large glacial lakes, a shifting climate, and the spread of cultural ideas across the Northern Plains.
Tracking the significance of KRF artifacts starts with correctly identifying the stone, which is difficult given the abundance of similar materials in North America. Artifacts made from other silica-rich rocks such as chert, chalcedony, and petrified wood can resemble KRF. Archaeologists mainly rely on naked-eye observations to distinguish KRF, including its translucent brown colouration, splotches of white mineral inclusions, glass-like or conchoidal fracture patterns, and the presence of a white patina (outer coating). Larger pieces of KRF may even have plant fossils, similar to petrified wood, embedded within it. Identifying lithic materials based on visual inspection alone is usually not enough, however. Geochemical laboratory techniques can help to determine the unique elemental or mineralogical composition of a rock. The geochemistry of KRF is quite variable due to its organic origins so research efforts to characterize it and distinguish it from other rock types have had mixed results (see recent studies from Alberta and Saskatchewan). Ultraviolet (UV) fluorescence can also be used to tell some rock types apart, as some minerals emit specific colours of light when exposed to UV radiation. KRF was once thought to fluoresce a specific colour, which helped archaeologists identify it, but recent work suggests that it fluoresces a range of colours under longwave UV light from yellow-gray to orange with some specimens of KRF that don’t fluoresce at all. Researchers are continuing to explore reliable, non-destructive methods for provenance work (using geochemistry and mineralogy to link an artifact to its original quarrying location).
The chain of interactions that transported KRF to Alberta and other far-reaching regions thousands of years ago is remarkable. KRF cobbles, cores, and tools were passed between countless hands to get from the quarries to the people who used the stone on a daily basis. The presence of KRF and any other exotic material at archaeological sites therefore signals a rich history of human connection and an incredible journey across cultural landscapes of the past.
For more information:
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Steuber, K.I. 2018. Geochemical Characterization of Brown Chalcedony during the Besant/Sonota Period. Ph.D. dissertation, Department of Archaeology and Anthropology, University of Saskatchewan, Saskatoon, Saskatchewan.
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