Aegirine is a sodium-rich pyroxene that typically forms long, slender, sharp prismatic crystals that are highly sought after by mineral collectors. It is most frequently identified by its distinct dark green to black color and high luster, often found embedded in alkaline igneous rocks like nepheline syenite. Large, terminated blades from localities like Mont Saint-Hilaire are considered world-class display specimens.
Is this aegirine?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch aegirine with a known reference. Aegirine sits at Mohs 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale yellowish gray.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to slightly resinous.
- 4Match the color rangeCompare against the expected color range: green, dark green, black, brown, greenish black, reddish brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular.
Often confused with
Aegirine vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Aegirine leaves pale yellowish gray, Augite leaves gray-green.
How to tell apart: Streak differs, so Aegirine leaves pale yellowish gray, Hornblende leaves grayish-white.
How to tell apart: Streak differs, so Aegirine leaves pale yellowish gray, Epidote leaves grayish white.
Often found alongside aegirine
Minerals reported to co-occur with aegirine. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaFe³⁺Si₂O₆
- Mohs hardness
- 6
- Density
- 3.50-3.60 g/cm³
- Streak
- Pale yellowish gray
- Luster
- Vitreous to slightly resinous
- Transparency
- Translucent to opaque
- Crystal system
- Monoclinic
- Crystal habit
- Acicular
- Cleavage
- Good on {110}, (110) ^ (110) ~87°; parting on {100}
- Rarity
- Common
- Uses
- Collector, Scientific research
- Host rock
- Common in alkalic igneous rocks, carbonatites, and pegmatites
Where rockhounds find aegirine
2 mapped spotsClassic worldwide localities
- Pitcairn, Russell, and LaSalle, St. Lawrence Co., and at Natural Bridge, Jefferson Co., New York, USA
- Magnet Cove, Hot Spring Co., and from Granite Mountain, near Little Rock, Pulaski Co., Arkansas, USA
- Bear Paw Mountains, Hill Co., Montana, USA
- Rundemyr, near Kongsberg, Norway
- Skaadoe, near Brevik, Norway
- Låven and other islands, Langesundsfjord, Norway
Field-hunting tip
Where it forms: Common in alkalic igneous rocks, carbonatites, and pegmatites. If you start seeing potassic feldspar, nepheline, riebeckite in float, you are in the right ground. Typical habit: acicular. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Montana, New York. Start trip planning there.
Common questions
How do you identify aegirine?+
Where is aegirine found?+
Can I find aegirine in the United States?+
What rocks look like aegirine?+
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Find aegirine on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
