Evidence of the anthropogenic origin of the ‘Carmel sapphire’ with enigmatic super-reduced minerals

Abstract Corundum with inclusions of enigmatic super-reduced minerals was found in mineral separates received as a result of alluvial sediment exploration near Mt Carmel, Israel by the Shefa Yamim Company. This corundum, registered as ‘Carmel sapphireTM’, has been an object of numerous publications by W. Griffin's scientific team, in which they propose a questionable hypothesis of sapphire formation at the crust–mantle boundary with the participation of CH4+H2 fluids. Typically the Carmel sapphire is in small fragments of breccia with white cement, which in the opinion of Griffin et al. is a carbonate-cemented volcanic ash. Our investigation of the ‘white breccia’ showed that it consists of unsorted angular fragments of Carmel sapphire from ~1 μm to 7 mm in size cemented by aluminium hydroxides (bauxite) and is a waste product of the fused alumina process, i.e. it has an anthropogenic origin. Phases typical for slags of fused alumina production and metallurgical slags were identified in the ‘white breccia’. Carmel sapphire has numerous microscopic spherical inclusions of Si–Fe alloy indicating that the removal of Si and Fe from the corundum melt occurred at a temperature >2000°С. Osbornite, TiN, from Carmel sapphire has a chemical zonation characteristic of osbornite from fused alumina with enrichment of central zones in carbon. Comparison of the growth heterogeneity of Carmel sapphire and ‘electrocorundum’ indicates that the crystallisation of the corundum melt proceeded in a similar way. Unfortunately, in the case of Carmel sapphire from the Carmel locality, the contamination of geological samples with anthropogenic material has led to popularisation of biased views.