Aegirine-augite is a solid-solution intermediate member of the pyroxene group between aegirine and augite. It typically forms dark, elongated prismatic crystals in alkaline igneous environments and can often be identified by its characteristic greenish-black color and vitreous luster.
Is this aegirine-augite?
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-augite with a known reference. Aegirine-augite 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. Aegirine-augite leaves a greenish-gray streak.
- 3Read the lusterHold the specimen under a strong light. Aegirine-augite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: black, greenish-black, dark green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, often elongated or acicular.
Often confused with
Aegirine-augite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Aegirine-augite leaves greenish-gray, Aegirine leaves yellowish-grey.
How to tell apart: Streak differs — Aegirine-augite leaves greenish-gray, Augite leaves grayish white.
How to tell apart: Streak differs — Aegirine-augite leaves greenish-gray, Hornblende leaves grayish-white.
Often found alongside aegirine-augite
Minerals reported to co-occur with aegirine-augite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,Ca,Mg,Fe²⁺,Fe³⁺,Al)₂Si₂O₆
- Mohs hardness
- 6
- Density
- 3.4-3.6 g/cm³
- Streak
- Greenish-gray
- Luster
- Vitreous
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Often Elongated or Acicular
- Cleavage
- Good in 2 Directions
- Rarity
- Common
- Uses
- Collector, Petrological Study
- Host rock
- Alkaline Igneous Rocks, Syenites, Nepheline Syenites
- Typical price
- $10-60 for typical specimens
Where rockhounds find aegirine-augite
Classic worldwide localities
- Norway
- Canada
- USA
- Russia
- Greenland
Field-hunting tip
Look in alkaline igneous rocks, syenites, nepheline syenites country — that is the host setting where aegirine-augite typically forms. If you start seeing nepheline, orthoclase, arfvedsonite in float, you are in the right ground. Field specimens usually show a prismatic crystals, often elongated or acicular habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify aegirine-augite?+
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Find aegirine-augite on the map
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