Mineral might have been sought for its combustion enhancing properties rather than as black pigment
Manganese dioxide minerals have been found at a number of Neanderthals sites in Europe, including Pech-de-l’Azé I in the Dordogne region of southern France. The site is around 50,000 years old, predating the arrival of modern humans in Europe. Over the last sixty years, the site has yielded several hundred small ‘blocs’ of black mineral, thought to be manganese dioxide, and totaling 750 gm in weight. The majority have been ground to obtain powder.
The long-standing view is that powdered manganese dioxide was used as a black pigment, but this view is challenged in a newly-published study. Although manganese dioxide minerals are reasonably abundant, it would have been far easier for Neanderthals to use charcoal and soot from their campfires as black pigment. Also, the evidence from other sites suggests that Neanderthals favoured manganese dioxide over other locally-available manganese minerals, even though the latter would yield equally-satisfactory black pigment. This led the researchers to consider uses for which only manganese dioxide would suffice.
Manganese dioxide is not combustible, but it is a powerful oxidising agent and thus aids the combustion of other materials. The researchers found that when industrial powdered manganese dioxide was mixed with wood turnings, the latter ignited at a temperature of 250 degrees Celsius, over a hundred degrees below the normal ignition temperature. Furthermore, the rate of charcoal combustion was substantially increased. As little as six percent by weight of manganese dioxide was required. The same results were obtained with powder obtained from the Pech-de-l’Azé I blocs.
Based on these experiments, the researchers concluded the Neanderthals’ chief use for manganese dioxide was for starting fires rather than pigment. With archaeological evidence for fireplaces and the production of manganese dioxide to powder, they suggest that the Neanderthals at Pech-de-l’Azé I were able to produce fire as required rather than having to make opportunistic use of lightning strikes and forest fires.
Heyes, P. et al., Selection and Use of Manganese Dioxide by Neanderthals. Scientific Reports 6 (22159 ), doi:10.1038/srep22159 (2016)