A tonstein is a thin, continuous band of hardened claystone found embedded within coal seams. Formed from volcanic ash falls that settled into ancient peat swamps, these layers are chemically distinct and laterally extensive. Geologists and mining engineers use tonsteins as reliable stratigraphic marker horizons to correlate coal beds across large mining districts and track fault displacements.
Heard on the job
We hit the main tonstein band right on schedule, which confirms we're still driving in the upper seam.