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A modest experimental program indicates that Knife River flint, an exceptionally fine-grained stone in raw form, can be successfully thermally pretreated at temperatures around 225°-250°C (437°-482°F). Heating greatly improves flaking qualities, yielding a material judged second only to volcanic glasses in flaking properties. Temperatures above 275°C induce marked weakness and brittleness in the stone. Heating yields the following observable changes: waxy luster and frequent ripple marks in fresh flake scars, a distinct darkening in color, and decreased translucency. The stone tool collection from the Lower Hidasta Village site (32ME10) (A.D. 1680-1780) indicates that heat treatment was selectively practiced with KRF tools requiring pressure flaking, occurring most commonly in arrowpoints.
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Stanley A. Ahler (1983) studied this question.
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