The identification of granitic Fire-Cracked Rocks using luminescence of alkali feldspars

The question of Fire-Cracked Rock (FCR) in Woodland contexts has become arl ir,important and controversial topic iii Western il Greet Lakes archaeolog y. There are no clear and widely accepted criteria for distinguishing FCR w hen the rocks show no observable characteristics associated with fire (heat ing and cooling. To help overcome this shortcoming, we analyzed both thermo luminescence (TL) and the optically stimulated luminescence (OSL) of alkali feldspar grains from a series of six samples of FCR from rite Hannaford si te in northern Minnesota. A geologic unheated specimen, om the same geograp hic area was used as a control ol sample. A comparison of the luminescence (TL aid OSL) intensities of both natural and natural plus artificial dose s ignals allowed us to demonstrate that the six selected samples of FCR had b een effectively heated nt the time of archaeological settlement. The good a greement between the TL and OSL results suggests that the OSL method is a v iable alternative to TL for the identification of FCR. The OSL method requi res less material, can be applied to a large number of samples, nod is more cost-effective.