Four millennia of garnet trade in Northeast Africa—chemical analysis of ancient and Late Antiquity beads from Lower Nubian sites

Raman spectroscopy and laser ablation-inductively coupled plasma-mass spectrometry were used to characterize the chemical composition of 34 red garnet beads from Lower Nubian sites, dated between about 3200 BCE and 600 CE. All beads from the A-Group to the Meroitic period feature a similar calcium-poor almandine composition (69%–78% almandine, 15%–22% pyrope, 2%–6% grossular, 3%–9% spessartine), which differs from other calcium-poor almandine garnet types, sourced mostly from Indian deposits in Antiquity. The Nubian beads constitute a new garnet type, named “cluster I”, featuring high yttrium (180 to 1205 ppm), moderately low chromium (13–70 ppm), and high scandium (119–213 ppm) concentrations. Their compositions match with previous and two new analyses from two alluvial garnet deposits, Wadi El-Haraz and Wadi Abu Dom, near the Fourth Cataract of the Nile in Upper Nubia, about 670 km as the crow flies from the Lower Nubian graves. Garnet trade between the Bayuda desert and Lower Nubia sites, and possibly even Egypt, flourished for almost four millennia. Northeastern Africa is the cradle for the oldest use of a gemstone that is harder than quartz—the red almandine garnet.

A Post-Meroitic bead, the youngest in the assembly, displays an unusual faceting, a diamond tipped drill hole, excellent polish, distinct short- and long-prismatic colorless mineral inclusions, and a calcium- and manganese-poor pyrope composition. This suggests that it was not of a local, Nubian, production, but imported, most probably from a South Asian site.