Thermal alteration of silica minerals: an archeological approach.
Extensive experiments indicate that the application of heat to flint materials may have conferred an advantage to primitive man in the manufacture of chipped-stone implements. When Florida cherts are slowly heated to between 350 degrees and 400 degrees C and maintained at this temperature for sustained periods, a desirable change occurs in the fracture properties. This alteration takes place when the melting point of the impurities within the intercrystalline spaces is reached; thus the microcrystals of quartz are fitted closer together when materials other than quartz serve as fluxes.
Purdy
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Brooks
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