I’ve knapped a bunch of KRF. Not an easy one to work. Totally unforgiving. One mistake and you are finished. Very few types of flint will hold an edge like KRF. It’s the tool steel of flint. Actually, it’s not flint at all. KRF is silicified lignite. The source was a large cattail swamp in the process of turning to coal when it was covered with volcanic ash. Silica from the ash converted the lignite in KRF. The deposit was later eroded out and deposited in Dunn and Mercer counties in N Dak. The whitish specks you see in KRF are remains of cattails.