gems, ancient gems, glyptic, archaeology, archaeogemology, Ethiopia, Red Sea, Eritrea, olivine basalts, geology, analytical

The island of Kod Ali is a small diatreme cone lying close to the Ethiopian coast at latitude 13° 57′ N, longitude 41° 49′ E. This volcanic structure, produced by geologically Recent volcanic activity, consists, almost entirely, of pyroclastic debris. Evidence of a liquid phase is confined to the thin veneers of markedly alkalic olivine basalt which coat many of the abundant gabbroic, pyroxenitic and lherzolitic fragments found on the island. As silicic inclusions are completely absent and as the alkalic liquid phase and the “tholeiitic” inclusions are seemingly genetically unrelated, it is proposed that the latter might have been derived from a tholeiitic plutonic layered sequence that underlies the tholeiitic basalts of an “oceanic” Red Sea floor.