CHARACTERISTICS AND GENESIS OF EL SAUZ CHERT, AN IMPORTANT PREHISTORIC LITHIC RESOURCE IN SOUTH TEXAS

Stone tools ranging in age from Early Archaic (3500–6000 B.C.) to Late Prehistoric (A.D. 700 to historic times), made of a distinctive light gray but sometimes colorful chert, have been identified in private collections in south Texas for at least 50 years. The source of this stone, known in the archeological literature as “El Sauz chert,” are two small bedrock outcrops in Starr County associated with altered rhyolitic ash of the Catahoula Formation. Physical characteristics, field evidence and major element chemical composition are used to infer an in situ origin of the chert associated with the devitrification of the volcanic ash and the remobilization of silica by ground and meteoric water. Distinctive characteristics of El Sauz chert include abundant vugs, opalized veins, smeared colorations, high aluminum content, and pale yellowish-green fluorescence under short-wave ultraviolet light. These geologically distinctive characteristics distinguish this material from other cherts and, as a result, have important implications for archaeologists interested in prehistoric exchange and resource procurement