A NEW NONDESTRUCTIVE METHOD FOR ANALYZING ANCIENT OIL SHALE SEALS AND SCARABOIDS: MEASURING EOM (EASILY OXIDIZED MATERIAL) BY SEM-EDS

Six large (33.5x33.5 mm to 46x44 mm) conical stone stamp seals and scaraboids as well as three smaller (15x13 mm to14.2x18.5 mm) common-size seals engraved with scenes of animals and, in some cases, combined with human figures carved from pieces of oil shale, have been recovered from the antiquities market in Jerusalem. All of the seals, representative of Canaanite and Israelite glyptic motifs, are dated from the 11th-9th century BCE. The seals originate from the Israeli synclinal structures of chalky bituminous rocks of Upper Cretaceous (Campanian-Maastrichtian) age that outcrop in the Judean desert, northeastern Negev and some localities east of the Jordan River. Modern methods for analyzing oil shales, particularly with respect to organic content, are destructive; we applied a new nondestructive technique in our analyses. The seals were examined by SEM-EDS and organic carbon values were obtained directly from them; however, one seal was analyzed using the (destructive) potassium dichromate oxidation method (PDOM). The organic carbon values obtained were 24.9% by SEM-EDS and 25% EOM, determined by the PDOM method. A fresh sample of oil shale that contained 22.3% organic matter (EOM, determined by the PDOM method) gave an organic carbon value of 22% by SEM-EDS analysis. Organic carbon values obtained by SEM-EDS analysis are therefore in agreement with organic matter EOM results.