noun · 2 senses · updated from the 2026-07-25 local source snapshot
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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.
Definition source: English Wiktionary via Wiktextract
Usage: countable, uncountable
Topics: geography, geology, natural-sciences
No example sentence was provided for this meaning.
Meaning relationships
Synonyms: none provided
Antonyms: none provided
2
noun
Meaning 2
Any indurated argillaceous rock that stands out within coal measures as a distinctive marker horizon.
Definition source: English Wiktionary via Wiktextract