Silicates — pyroxene group · Sourced PROFILE
Aegirine
NaFe³⁺Si₂O₆
A dark sodium–iron pyroxene characteristic of alkaline rocks and documented in the rare-mineral assemblages of Dara-i-Pioz.
AT A GLANCE
- Formula
- NaFe³⁺Si₂O₆
- Crystal system
- Monoclinic
- Space group
- C2/c
- Mohs hardness
- 6
- Density
- 3.50–3.60 g/cm³
- Optical character
- Biaxial (−), with Ca–Mg–Fe²⁺-rich material potentially biaxial (+)
CRYSTALLOGRAPHY
Crystal form & structure
Prismatic crystals with blunt to steep terminations, commonly length-striated; also acicular sprays, fibrous aggregates and radial concretions.
HAND-SAMPLE PROPERTIES
Physical properties
- Cleavage
- Good on {110}; parting on {100}
- Fracture
- Uneven
- Tenacity
- Brittle
- Streak
- Pale yellowish grey
- Luster
- Vitreous to slightly resinous
- Transparency
- Translucent to opaque
- Observed colours
- Dark green, greenish black, reddish brown or black
LIGHT & OPTICS
Optical properties
- Optical class
- Biaxial (−), with Ca–Mg–Fe²⁺-rich material potentially biaxial (+)
- Refractive index
- nα 1.722–1.776; nβ 1.780–1.820; nγ 1.795–1.836
- Fluorescence & electrical behaviour
- No diagnostic fluorescence is reported in the cited profile.
GEOLOGICAL SETTING
Formation
Forms in alkaline igneous rocks, carbonatites and pegmatites, and through sodium-rich metasomatism.
MINERAL COMPANY
Common associations
Potassic feldspar, nepheline, riebeckite, arfvedsonite, aenigmatite, astrophyllite, eudialyte, sérandite and apophyllite
FIELD NOTES
How to identify it
Dark green-black prismatic habit, hardness 6, good near-right-angle pyroxene cleavage and strong pleochroism are useful clues; chemistry or diffraction is needed for confirmation.
NAME & HISTORY
Where the name comes from
Named for Ægir, the Scandinavian sea god, after the Norwegian locality where it was first described.
SCIENTIFIC SOURCE
Handbook of Mineralogy — Aegirine
External reference; factual profile paraphrased and attributed. Copyright remains with the publisher.
PROVENANCE
Documented occurrences
Dara-i-Pioz alkaline complex, Alai Range · Aegirine is a principal component of a quartz–albite–aegirine rock containing the rare minerals baratovite and miserite. The public record is intentionally limited to approximate locality.
Sourced · ApproximateLocality precisionThe mineralogy of a unique baratovite- and miserite-bearing quartz–albite–aegirine rock from the Dara-i-Pioz Complex