Status: 1 Treffer • Seite 1 von 1 • 10 Artikel pro Seite
2016-07-03 09:22:50 • ID: 1450
A Handaxe made of Ignimbrite
As the pyroclastic material settles it can build up thick layers, and if the temperature is sufficiently high (> 535°C) it can weld into rock. Ignimbrites are made of a very poorly sorted mixture of volcanic ash (or tuff when lithified) and pumice lapilli, commonly with scattered lithic fragments.
The ash is composed of glass shards and crystal fragments. While most volcanic rocks are found close to the eruptive source, ignimbrite of reasonable thickness can often be found tens to hundreds of kilometers from the site of eruption. Ignimbrites may be white, grey, pink, beige, brown or black as shown in this post, depending on their composition and density.
Many pale ignimbrites are dacitic or rhyolitic. Darker colored ignimbrites may be densely welded volcanic glass or, less commonly, mafic in composition.
During the Paleolithic Ignimbrites were used in East Africa, allways in small quantities since the Oldowan, especially at Melka Kunture, but also at Gona, Ethiopia and East Turkana (Koobi Fora), Kenya.
During the Earliest Paleolithic, volcanic rocks in general, allways coming from small distances, such as lavas, were common, and in many areas basement quartzes and quartzites were also used. In North Africa, as at Ain Hanech, fine-grained limestones were also a major source of raw material. At some sites, cherts/flints were also locally available in larger quantities (some Bed II sites at Olduvai and at Ain Hanech), but generally their frequency is rather low.
During the Acheulian and the MSA, ignimbrites in Africa were still constantly in use, but in negligables quantities. In Europe, the only published handaxe made from ignimbrites is known from the assemblage at Pontnewydd; Wales / UK (ca 250 k.a.).
Two fine Middle Paleolithic"Keilmesser" from the Middle European Micoquian, made from Dalarna-ignimbrite were found at Salzkotten-Oberntudorf near Paderborn in Westphalia (ca 80-40 k.a.).
The handaxe displayed here comes from Southern Mauritania and is a perfect 10 cm long cordiform made of this volcanic raw material, indicating that some fine grained ignimbrites were appropriate for producing even the finest handaxe, comparable to much later examples from the MTA.