Mineralogy of the ceramic slags from the Bronze Age funerary site at Lăpuş (NW Romania)

Abstract

A Bronze Age (13–12th century B.C.) necropolis and cult area in Lăpuş (NW Romania) has been studied. The mound investigated during the present campaign covered a multi-phased wooden cult building containing bronze objects, ceramic potshards and slag pieces. The latter have a mammillary smooth surface, irregular shape and a high porosity. Optical microscopy reveals a colourless to brown vitreous mass, full with various-sized pores making up to 40 vol.% of the total slag. The glass includes relic phases, e.g., quartz, partly melted plagioclase and rutile, rare zircon, ilmenite and magnetite-rich spinel. Cristobalite and various silicates were formed within the glass and at the wall of the vesicles during cooling. The latter include fayalite, ferrosilite, magnetite-dominated spinel, hematite, clinopyroxene, mullite and cordierite. About 1/3 of the total volume of the slag consists of glass with a wide variety of SiO2 ranging from 49 to 76 wt.%. It is inhomogeneous, with local enrichment in Fe, Ca, Mg, Ti and K. The pore structure, the partial melting of plagioclase and rutile, the newly formed SiO2 polymorphs (cristobalite) and the Fe(Al) silicates indicate, all indicate maximum temperatures of 1100–1200°C for the fire generating the slags. The slags are not related to any metallurgical but to an anthropogenic pyrometamorphic process and formed as a result of overfiring some ceramic vessels which may have contained ritual offerings. Intentionally initiated firing of the wooden structures is the most likely the agent of this high temperature. The slags resemble buchites and can be termed “ceramic slags”