The rock of the Tellure mine in Sainte-Marie-aux-Mines in the Haut-Rhin region is composed of gneiss, a metamorphic rock formed at depth during continental collisions. Gneiss sometimes resembles granite but can be recognised by the parallel alignment of strata of quartz, feldspar, mica and especially silver. In the 16th century, silver ore was used to make coins whose value depended on the silver content. The rappe was used in the Rhine Valley, the ecu and denarius in the kingdom of France and the thaler in the Holy Roman Empire. Imported into the New World, the thaler is the origin of the word dollar.