RocksdayAugite vs Hornblende
How to tell them apart
The most common pyroxene, forming stubby black crystals in basalt and gabbro.
Photo: Didier Descouens, CC BY-SA 4.0
A common black amphibole and the dark specks in many granites and diorites.
Photo: Shannon Heinle, CC0
Quick tests
- Streak (rub on unglazed porcelain): Augite leaves a greenish gray streak; Hornblende leaves gray-green.
Key differences
- Hornblende is longer and its cleavages meet at 56°/124°.
- Augite is stubbier with cleavages at nearly 90°.
Side by side
| Property | Augite | Hornblende |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 5.5–6 | 5–6 |
| Luster | Vitreous to dull | Vitreous |
| Streak | Greenish gray | Gray-green |
| Colors | Black, Green, Brown | Black, Green, Brown |
| Crystal system | Monoclinic | Monoclinic |
| Specific gravity | 3.2–3.6 | 3–3.4 |
| Formula | (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)₂O₆ | Ca₂(Mg,Fe,Al)₅(Al,Si)₈O₂₂(OH)₂ |
| Found in | Basalts worldwide; Mount Vesuvius, Italy | Granites and diorites worldwide; Amphibolites |
Properties that are the same for both are grayed out.
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 →How to identify hornblende
- Black to dark green elongated prisms.
- Two cleavages meeting at about 56° and 124°.
- Shiny, splintery breaks.
Crystal system: Monoclinic
Full Hornblende guide →More comparisons
Could you tell them apart from a blurry close-up?
Play today's Rocksday