The aboriginal thermal processing of Bald Eagle Jasper in Central Pennsylvania is described in terms of the chemical and physical changes that accur in this material. Heat tratment in shown to transform the jasper´s geothite component to hematite and to improve its workability by reducing its fracture toughness by one half. This is accompanied by a yellow to red color change. The role of thermal alteration in the local lithic technology is inferred from laboratory heating experiments and from an analysis of lithic artifacts from the Houserville site a jasér workshop. The prehistoric utilization of this material is analyzed from a regional perspective. The results have implications for aboriginal social organization in Central Pennsylvania.