Microcline
A triclinic K-feldspar mineral, KAlSi₃O₈, commonly found in granites and pegmatites.
Language and route: German scientific formation ← Ancient Greek. Breithaupt’s German Mikroklin combines Greek μικρός ‘small’ and κλίνειν ‘to incline’.
Literal gloss: slight inclination
The name and its history
August Breithaupt · 1830
- What does the word literally mean?
- The transmitted name is Breithaupt’s German Mikroklin combines Greek μικρός ‘small’ and κλίνειν ‘to incline’. The short gloss ‘slight inclination’ is a guide to the naming allusion, not by itself a modern mineralogical definition.
- What did the original author mean?
- Breithaupt applied the name in 1830 to Norwegian feldspar material from the Arendal and Stavern areas, recognising a slight deviation from the symmetry expected of orthoclase.
- Why was the name needed?
- Breithaupt explicitly criticised the older practice of using “feldspar” simultaneously as the name of a genus and a species. His 1830 reorganisation, including microcline, made a distinct taxonomy necessary as measured crystallographic differences multiplied.
- What evidence supported the original concept?
- Crystal morphology and angular measurement provided the original basis; modern twinning and diffraction criteria came later.
- How has geology changed the concept?
- Microcline, orthoclase and sanidine may share the same ideal chemical formula but differ in crystal structure and Al–Si ordering.
Further historical context
Breithaupt applied the name in 1830 to Norwegian feldspar material from the Arendal and Stavern areas, recognising a slight deviation from the symmetry expected of orthoclase.
Breithaupt explicitly criticised the older practice of using “feldspar” simultaneously as the name of a genus and a species. His 1830 reorganisation, including microcline, made a distinct taxonomy necessary as measured crystallographic differences multiplied.
Crystal morphology and angular measurement provided the original basis; modern twinning and diffraction criteria came later.
Microcline, orthoclase and sanidine may share the same ideal chemical formula but differ in crystal structure and Al–Si ordering.
Related names
Orthoclase · Sanidine · Feldspar · Pegmatite
Sources
- Mindat, Microcline — Breithaupt (1830) — Name, original Norwegian material and structural meaning
- Mindat, Orthoclase — Haüy 1801 and Breithaupt 1823 — Haüy’s orthose and later orthoklas; modern species identity
- IMA–CNMNC, List of Mineral Names (updated September 2026) — Contemporary mineral-species standing; consult live master list
- Breithaupt (1830), original microcline article (digitised) — Original-paper access via Sofia museum bibliography; text of genus/species argument partially consulted