Aegirine is a sodium iron silicate mineral (NaFe³⁺Si₂O₆) belonging to the pyroxene group, known for its dark green prismatic crystals and occurrence in alkaline igneous rocks. It is both scientifically significant and visually striking, often forming sharp, spear-like crystals.
🌍 Origins and Naming
- First Described: 1835 by H.M.T. Esmark from Låven, Langesundsfjorden, Norway.
- Name Origin: Named after Ægir, the Norse sea god, reflecting its discovery in coastal Norway.
- Synonym: Historically called acmite (from Greek akmē, “point”), referencing its pointed crystal habit.
🔬 Chemical and Structural Properties
- Formula: NaFe³⁺Si₂O₆
- Crystal System: Monoclinic (clinopyroxene subgroup)
- Color: Dark green, greenish-black, brownish-black, or reddish-black
- Habit: Long, slender prismatic crystals, often in sprays or radiating groups
- Hardness: ~6 on Mohs scale
- Specific Gravity: 3.50–3.60
- Luster: Vitreous to slightly resinous
- Streak: Yellowish-gray
- Optical Properties: Strong pleochroism (emerald green to brownish tones)
⚙️ Geological Occurrence
Aegirine typically forms in:
- Alkaline igneous rocks (nepheline syenites, peralkaline granites, phonolites)
- Pegmatites associated with alkali-rich environments
- Metamorphic rocks under high-pressure conditions
Notable localities:
- Norway (Buskerud, Langesundsfjorden) – type locality
- Mount Malosa, Malawi – famous for spectacular crystals
- Kola Peninsula, Russia – large alkaline complexes
- Magnet Cove, Arkansas, USA – alkaline igneous deposits
💎 Collector and Scientific Significance
- Petrology: Indicator mineral in alkaline magmatic systems, helping geologists understand geochemical differentiation.
- Collectors: Sharp, lustrous crystals are highly prized, especially when associated with feldspar, quartz, or zircon.
- Scientific Value: Provides insights into sodium-rich magmatic environments and rare earth element associations.
📖 Conclusion
Aegirine is a mineral that bridges scientific importance and aesthetic appeal. Its spear-like crystals, dark green coloration, and role in alkaline igneous petrology make it both a collector’s treasure and a geologist’s tool. Historically known as acmite, aegirine remains a striking example of how mineralogy connects natural beauty with deep geological processes.
In short: Aegirine is a sodium iron silicate pyroxene, famous for its dark green spear-like crystals and role in alkaline igneous rocks.
