tonstein

noun

1. (countable, uncountable)A hard, compact, kaolinite-rich claystone formed by the diagenetic alteration of volcanic ash, usually occurring as thin, laterally persistent layers interbedded with coal seams.

   “Tonsteins, which are altered volcanic ash, mark instantaneous events over large areas and thus are excellent time markers for basin analysis.”

   “Because the zircons of the Upper Banner and Hitchins tonsteins (as well as other sampled Pennsylvanian tonsteins) lack radiogenic inheritance, the may derive from the magmatic arc of Sinha and Zietz, which was farther east and outboard of the North American continent at that time.”

2. (countable, uncountable)Any indurated argillaceous rock that stands out within coal measures as a distinctive marker horizon.

   “In Figure 13, all data points of the tonstein samples fall within the CHARAC range.”