4.3 inch long Shoshonean knife form from a private ranch in south central Wyoming and made from tiger chert from the Green River Formation in the Blacks Fork area of Wyoming and the Sheep Creek area of the Unita Mountains in Utah. The sub parallel bands in tiger chert represent preserved lake varves. The darker bands are almost pure silica (opalitic chert) and are interbedded with lighter bands of fine clastic material (porcellanite). John Branney Collection.
3.8 inch long ultrathin knife form made from a Georgetown variety of Edwards chert and surface found in Coryell County, Texas. This prehistoric ultrathin knife form measures 95 millimeters long, 48 millimeters wide, and 5 millimeters or less in thickness. The width to thickness ratio is 9.6, well within the set range for defining ultrathin knife forms. John Branney Collection.