Pegmatite
A very coarse-crystalline rock or vein material; especially common in granitic systems, but the descriptor need not imply granitic composition.
Language and route: French pegmatite, subsequently international geological usage. French scientific pegmatite, based on Greek pêgma, ‘something fastened or joined’, referring originally to graphic intergrowths of quartz and feldspar.
Literal gloss: something fastened together
The name and its history
René-Just Haüy (early documented use) · early nineteenth century; text attested in 1823
- What does the word literally mean?
- A joined framework; originally a reference to intergrown crystals, not directly to crystal size.
- What did the original author mean?
- Haüy used pegmatite for quartz–feldspar graphic intergrowth, rather than for every coarse-grained vein rock. A later text of 1823 records this early restricted usage.
- Why was the name needed?
- A rock texture with quartz interlocking through feldspar demanded a descriptive term different from names based on bulk mineral composition.
- What evidence supported the original concept?
- Interpenetrating crystal texture in graphic granite, recognisable by the script-like appearance of sections through quartz within feldspar.
- How has geology changed the concept?
- Use broadened during the nineteenth century to remarkably coarse-crystalline veins and rocks even where the original graphic intergrowth is absent. BGS uses pegmatite as a coarse-crystal/vein descriptor and encourages mineral qualifiers.
Further historical context
A literal gloss ‘bound together’ makes sense in the original graphic-texture context; the later modern definition ‘very large crystals’ did not motivate Haüy’s original choice.
Historians distinguish Haüy’s older restricted term from later broader usage; some secondary sources differ over 1822 versus 1823, so a precise first date is not claimed here.
Editorial qualification
Original Haüy publication priority is not established here; sources quote an 1823 edition. Modern pegmatite is a texture/occurrence term, not automatically a granite.
Related names
Aplite · Granite · Feldspar · Quartz · Tourmaline · Granitic · Microcline · Muscovite · Albite · Microgranite · Tonalite · Syenite
Sources
- GIA (2025), Gem Granitic Pegmatites — Haüy 1823 wording and the historical graphic-granite usage
- British Geological Survey, Rock Classification Scheme: pegmatite — Operational lithological definition
- Académie française, Dictionnaire: pegmatite — French lexical derivation from Ancient Greek
- Landes (1933), Origin and Classification of Pegmatites, American Mineralogist — Early historical review of changing pegmatite definitions