Diorite
Plutonic intermediate rock dominated by plagioclase and mafic minerals; distinguished from gabbro partly by plagioclase composition.
Language and route: French diorite formed from Greek diorízein. French diorite formed from Greek diorízein
Literal gloss: to distinguish, delimit
The name and its history
Alexandre Brongniart; exact original appearance requires source verification · Not securely established
- What does the word literally mean?
- Literal naming sense: to distinguish, delimit. Immediate language/formation: French diorite formed from Greek diorízein. Historically an act of petrographic distinction, not “two rocks” from a prefix di-.
- What did the original author mean?
- Brongniart’s name served to separate a set of dark, crystalline rocks that were being confused under older, more general rock labels.
- Why was the name needed?
- Growing petrographic categories needed a way to distinguish feldspar–hornblende-rich material from granite, syenite and greenstone.
- What evidence supported the original concept?
- Macroscopic mineral assemblage and comparative descriptions preceded precise modal and chemical classification.
- How has geology changed the concept?
- IUGS places diorite with gabbro in some QAP fields and distinguishes them using plagioclase An-content and mafic assemblage; the etymology is not itself a mineralogical criterion.
Further historical context
Brongniart’s name served to separate a set of dark, crystalline rocks that were being confused under older, more general rock labels.
Growing petrographic categories needed a way to distinguish feldspar–hornblende-rich material from granite, syenite and greenstone.
Macroscopic mineral assemblage and comparative descriptions preceded precise modal and chemical classification.
IUGS places diorite with gabbro in some QAP fields and distinguishes them using plagioclase An-content and mafic assemblage; the etymology is not itself a mineralogical criterion.
Editorial qualification
Do not give an unverified first-publication year as established.
Related names
Gabbro · Tonalite · Syenite · Plagioclase · Hornblende · QAPF classification
Sources
- Collins English Dictionary, diorite — French borrowing and Greek *diorizein*
- BGS, Rock Classification Scheme — Modern descriptive rock-naming principles and definitions
- USGS, Lithologic classification of geologic map units — Modal definitions and named plutonic-rock categories
- IUGS / Le Maitre et al. (2002), Igneous Rocks: A Classification and Glossary of Terms, ch. 3 — Authoritative IUGS rock-name history and bibliographic attributions