Research / Geoscience / Language
Oligoclase
A sodium-rich plagioclase compositional variety between albite and andesine.
Language and route: German mineralogical compound from Greek. German-derived oligoclase, Greek ὀλίγος (olígos), ‘little’, + κλάσις (klásis), ‘fracture’
Literal gloss: little fracture
The name and its history
August Breithaupt · 1826 (secondary mineral catalogue)
- What does the word literally mean?
- The gloss ‘little fracture’ describes the linguistic allusion. The original name and its modern scientific definition must be kept distinct.
- What did the original author mean?
- Breithaupt’s cleavage-related name distinguished feldspar specimens whose fracture/cleavage characteristics appeared different.
- Why was the name needed?
- Observed distinctions among feldspar specimens needed stable mineralogical categories.
- What evidence supported the original concept?
- Mineral crystal cleavage and material described from the Stockholm area.
- How has geology changed the concept?
- Now a plagioclase compositional range, not an independent accepted species; the original fracture gloss should not be taken as a modern diagnostic compositional test.
Further historical context
The same Greek root oligo- appears in Oligocene, but there it once alluded to fossil species, not feldspar cleavage.
Related names
Albite · Plagioclase · Andesine · Oligocene
Sources
- Mindat, Oligoclase — Naming date, etymology and modern plagioclase standing