Experimental analysis on natural heated goethite from ponte di Veja (Mt Lessini, NE Italy)

The use of fire technology for transforming yellow goethite into red hematite was common, intentional and consolidated practice in Prehistoric settlements. Mineralogical structural analyses using X-ray powder diffraction (XRPD) and transmission electron microscopy (TEM) have been successfully employed for studying artificial hematite and for the estimation of the relevant transformation temperatures. Thermal treatments, over a temperature range of 250 up to 1000 degrees C, have been carried out on natural goethite (associated with quartz) collected from the palaeokarst caves at Ponte di Veja in North-Eastern Italy (Western sector of the Lessini Mountains) with the scope to compare the effects of heat treatment on natural goethite with synthetic goethite. This site provided extensively Fe-rich raw materials to the Upper Palaeolithic site Tagliente rockshelter. The mineralogical analysis demonstrated that selective broadening of some diffraction peaks occurs during the transformation for temperatures between 250 and 800 degrees C, confirmed by TEM analyses, in accordance with experiments executed on synthetic goethite samples.

Automated summary

The intentional use of fire technology to transform yellow goethite into red hematite was a common practice in Prehistoric settlements. Mineralogical structural analyses using XRPD and TEM were employed to study the relevant transformation temperatures. Heat treatment experiments on natural goethite demonstrated selective broadening of diffraction peaks between 250 and 800 degrees Celsius, similar to synthetic goethite samples.