# tonstein

> English word · Noun · IPA /ˈtʌnˌstaɪ̯n/

## Definitions
1. 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.
2. Any indurated argillaceous rock that stands out within coal measures as a distinctive marker horizon.

## Etymology
Borrowed from German Tonstein, from Ton (“clay”) + Stein (“stone”).

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/tonstein