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. Streak: greenish-gray.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: black, dark green, green, pale greenish yellow, greenish gray.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: anhedral grains, fibrous, prismatic.
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, so Aegirine-augite leaves greenish-gray, Aegirine leaves pale yellowish gray.
How to tell apart: Streak differs, so Aegirine-augite leaves greenish-gray, Augite leaves gray-green.
How to tell apart: Streak differs, so 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
- (Ca₀.₆Na₀.₄)(Mg₀.₆Fe₀.₄)Si₂O₆
- Mohs hardness
- 6
- Density
- 3.4-3.6 g/cm³
- Streak
- Greenish-gray
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Anhedral grains, fibrous, prismatic
- Cleavage
- Very good on {110}; parting on {100}
- Rarity
- Common
- Uses
- Collector, Petrological study
- Host rock
- Characteristic mineral of alkaline rocks, particularly syenites and iron-rich metamorphic and metasomatic rocks
Where rockhounds find aegirine-augite
Classic worldwide localities
- Norway
- Canada
- USA
- Russia
- Greenland
Field-hunting tip
Where it forms: Characteristic mineral of alkaline rocks, particularly syenites and iron-rich metamorphic and metasomatic rocks. If you start seeing nepheline, orthoclase, arfvedsonite in float, you are in the right ground. Typical habit: anhedral grains, fibrous, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify aegirine-augite?+
Where is aegirine-augite found?+
What rocks look like aegirine-augite?+
What minerals are found with aegirine-augite?+
What kind of rock does aegirine-augite form in?+
What is aegirine-augite used for?+
Find aegirine-augite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
