Blueschist
Schist containing blue sodic amphibole; also names a high-pressure, comparatively low-temperature metamorphic facies when explicitly qualified.
Language and route: Modern English compound blue + schist, referencing sodic blue amphibole (especially glaucophane). Modern English compound blue + schist, referencing sodic blue amphibole (especially glaucophane)
Literal gloss: blue schist
The name and its history
Edgar H. Bailey (historical attribution by IUGS SCMR) · 1962 (first printed page remains to be checked)
- What does the word literally mean?
- Immediate linguistic route: Modern English compound blue + schist, referencing sodic blue amphibole (especially glaucophane). Literal or inherited gloss: ‘blue schist’. An attested linguistic component is not by itself evidence of a historical scientist’s reason for naming this rock.
- What did the original author mean?
- Eskola’s earlier glaucophane-schist facies was debated as to whether glaucophane might coexist with greenschist-grade conditions; IUGS dates Bailey’s blueschist usage to 1962.
- Why was the name needed?
- The new facies terminology sought a reliably recognised high-P/low-T rock assemblage, favouring jadeite and lawsonite indicators amid competing stability interpretations.
- What evidence supported the original concept?
- Blue amphibole, lawsonite, jadeite and associated field relations supported facies debates; some 1960s writers argued overburden versus tectonic pressure and high pore-fluid pressure.
- How has geology changed the concept?
- Plate-tectonic subduction explains many occurrences, but IUGS distinguishes the colour-defined rock from an inferred facies, and prefers mineral-specific compound names when possible.
Further historical context
Eskola’s earlier glaucophane-schist facies was debated as to whether glaucophane might coexist with greenschist-grade conditions; IUGS dates Bailey’s blueschist usage to 1962.
The new facies terminology sought a reliably recognised high-P/low-T rock assemblage, favouring jadeite and lawsonite indicators amid competing stability interpretations.
Blue amphibole, lawsonite, jadeite and associated field relations supported facies debates; some 1960s writers argued overburden versus tectonic pressure and high pore-fluid pressure.
Plate-tectonic subduction explains many occurrences, but IUGS distinguishes the colour-defined rock from an inferred facies, and prefers mineral-specific compound names when possible.
Editorial qualification
Do not equate an early recorded description with a formal first coining; exact priority and historical wording remain unverified.
Related names
Schist · Greenschist · Eclogite · Amphibolite · Facies
Sources
- IUGS SCMR, high-pressure rock nomenclature, Bailey 1962 discussion — IUGS historical review of blueschist name, 1962 and competing pressure indicators
- Blake, Irwin and Coleman 1969, Blueschist-facies metamorphism related to thrust faulting — contemporary alternative pre-plate-tectonic pressure interpretation, abstract checked
- IUGS SCMR, High pressure/temperature metamorphic rocks — guidance on eclogite and blueschist rock-name versus facies-name distinction
- Eskola, The Mineral Facies of Rocks (1920), Norsk Geologisk Tidsskrift, 6:143–194 — identified original facies research publication, pages not independently checked