A vesicular volcanic rock is found in the Laacher See area, Eifel, West Germany, from which querns were made in prehistoric and later times. The rock actually is a leucite-nepheline tephrite to tephritic foidite and lies between the places of Mayen, Ettringen and Kottenheim with an area of about six square kilometres. The querns from Mayen were traded all over North West Europe. Quern fragments are frequently found in the Netherlands in settlements dated to the Iron Age, but they are more abundant found in Roman and Early-Medieval excavation complexes. Selection criteria for the use of this particular tephrite as raw material for quern making are obvious. The grinding capability of the vesicular quern surface is constantly renewed by wear. The valuable lava has a great extension and a sufficient thickness to support a major quern industry. Another feature is the situation of this tephrite occurrence near the important trade route, the river Rhine.