Argillite
Hard, indurated mudrock, commonly more consolidated than ordinary mudstone but without the characteristic slaty cleavage of slate.
Language and route: English via French argillite, from argile ‘clay’, ultimately Latin argilla; -ite scholarly suffix. English via French argillite, from argile ‘clay’, ultimately Latin argilla; -ite scholarly suffix
Literal gloss: clay-related stone
The name and its history
First geological naming act not verified · First geological printed use not verified
- What does the word literally mean?
- Immediate borrowing/formation pathway: English via French argillite, from argile ‘clay’, ultimately Latin argilla; -ite scholarly suffix. Linguistic gloss: ‘clay-related stone’. This is not automatically the original namer’s stated reason.
- What did the original author mean?
- Continental and English petrographers used clay-derived rock adjectives while field geologists struggled to classify very hard fine-grained rocks with variable splitting tendencies.
- Why was the name needed?
- The vocabulary needed room for lithified and sometimes weakly altered fine mudrocks without automatically calling them shale or slate.
- What evidence supported the original concept?
- Hardness, fine grain size, bedding, absence of strong fissility and absence of penetrative slaty cleavage; exact rock-grade distinctions can be transitional.
- How has geology changed the concept?
- USGS defines argillite between common mudrocks and true slate; some regional geological maps use the name more broadly or with a weak metamorphic implication.
Further historical context
Continental and English petrographers used clay-derived rock adjectives while field geologists struggled to classify very hard fine-grained rocks with variable splitting tendencies.
The vocabulary needed room for lithified and sometimes weakly altered fine mudrocks without automatically calling them shale or slate.
Hardness, fine grain size, bedding, absence of strong fissility and absence of penetrative slaty cleavage; exact rock-grade distinctions can be transitional.
USGS defines argillite between common mudrocks and true slate; some regional geological maps use the name more broadly or with a weak metamorphic implication.
Editorial qualification
First coinage/priority not independently established; historical narrative is a source-bounded reconstruction.
Related names
Sources
- USGS thesaurus: Argillite — Modern induration/fissility/slate distinction
- USGS, Lithologic classification of geologic map units — Alternative modern operational vocabulary, including mudrocks
- British Geological Survey, Rock Classification Scheme, Volume 3 overview — Modern descriptive sedimentary classification; does not establish historical first use