RocksdayAegirine vs Augite
The quickest way to tell Aegirine from Augite: Aegirine leaves a yellowish gray streak; Augite leaves greenish gray.
A sodium-iron pyroxene that forms black to greenish-black prisms in rocks that are poor in silica.
Photo: Ivar Leidus, CC BY-SA 4.0
The most common pyroxene, forming stubby black crystals in basalt and gabbro.
Photo: Didier Descouens, CC BY-SA 4.0
Quick tests
- Streak (rub on unglazed porcelain): Aegirine leaves a yellowish gray streak; Augite leaves greenish gray.
Key differences
- Augite is the common dark pyroxene of basalt and gabbro, not of nepheline syenites.
Side by side
| Property | Aegirine | Augite |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6 | 5.5–6 |
| Luster | Vitreous | Vitreous to dull |
| Streak | Yellowish gray | Greenish gray |
| Colors | Black, Green, Brown | Black, Green, Brown |
| Crystal system | Monoclinic | Monoclinic |
| Specific gravity | 3.5–3.6 | 3.2–3.6 |
| Formula | NaFeSi₂O₆ | (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)₂O₆ |
| Found in | Mount Malosa, Malawi; Mont Saint-Hilaire, Quebec | Basalts worldwide; Mount Vesuvius, Italy |
Properties that are the same for both are grayed out.
How to identify aegirine
- Black or dark green slender prisms.
- Two cleavages crossing at nearly 90°.
- Hardness about 6. Pale yellowish streak.
Crystal system: Monoclinic
Full Aegirine guide →How to identify augite
- Short, stubby black prisms with an eight-sided cross-section.
- Two cleavages at nearly right angles.
- Found in dark volcanic rocks.
Crystal system: Monoclinic
Full Augite guide →More comparisons
Frequently asked questions
What is the difference between aegirine and augite?
Aegirine is a mineral (NaFeSi₂O₆) with a Mohs hardness of 6 and a vitreous luster, usually black, green or brown. Augite is a mineral with a Mohs hardness of 5.5–6 and a vitreous to dull luster, usually black, green or brown.
How can you tell aegirine from augite?
Aegirine leaves a yellowish gray streak; Augite leaves greenish gray. Augite is the common dark pyroxene of basalt and gabbro, not of nepheline syenites.
Could you tell them apart from a blurry close-up?
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