It changes the matrix from a beautiful, transparent chalcedony to a granular, bluish-gray opaque quartz and the stone simply crushes when worked. The inclusions change little if at all. Gunflint Silica Gunflint Silica is filled with inclusions greatly differing in size and random placement. The grains can range from the finely ground size to infrequent 1 mm smooth margined. The variation in concentration of these inclusions creates materials which vary from transparent to very dark, sometimes a deep black.
Some examples have an almost transparent matrix with very few inclusions.
All thin specimens, however black, when held to the light show the chalcedonous background regardless of how heavily it is filled. Small particles can clump together to form rough edged, irregular masses. Some rocks contain sufficient hematite to exhibit red streaking. Historic literature has linked the source of this material to Gunflint Lake on the eastern end of the Border Lakes. This rock had ample sampling of Gunflint Silica but by no means was it of the quality found in many artifacts.