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Augite
Augite is inosilicate (pyroxene), (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)₂O₆. In the hand, it rates 5.5 to 6 on the Mohs scale, and it runs black and greenish black. Stubby black blocky prisms with nearly right-angle cleavages and an eight-sided cross-section, the standard dark mineral of basalt country.
The geology.
Augite carries the formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)₂O₆. It belongs to the monoclinic system. Catalogues list it as inosilicate (pyroxene).
It sits at 5.5 to 6 on the Mohs scale. The surface reads vitreous to dull. Light behaviour is opaque; translucent thin edges. Specific gravity runs 3.2 to 3.6. The streak is greenish gray. It breaks with two cleavages near 87°/93°; uneven fracture.
Stubby black blocky prisms with nearly right-angle cleavages and an eight-sided cross-section, the standard dark mineral of basalt country.
It reaches buyers as stubby blocky prisms, loose crystals from volcanic ash or grains in basalt and gabbro.
The origins.
Basalts and gabbros worldwide; collectible loose crystals erode from volcanic ash in Italy (Vesuvius), Mexico, Oregon (USA).
On value, the database notes: common; sharp loose crystals are inexpensive collector staples.
Traditional associations.
In energy work traditions, augite has little established lore; it is the workhorse dark mineral of volcanic rocks.
We keep this section because people ask. It sits below the geology on purpose, and none of it describes something the stone does.
Spotting the real thing.
Stubby black blocky prisms with nearly right-angle cleavages and an eight-sided cross-section, the standard dark mineral of basalt country.
| Looks like | How to tell them apart |
|---|---|
| Hornblende | Amphibole cleavages meet at 56°/124° and crystals are longer and shinier; augite's meet near 90° on stubbier blocks |
| Black tourmaline | Schorl is striated, glassy, with no cleavage |
| Diopside | Paler green pyroxene cousin, augite is the dark iron-rich field version |
At-home tests.
Before anyone talks you into a lab report, these are the checks worth doing yourself on augite.
| Test | What you should see |
|---|---|
| By eye | Cleavage faces meet near 90° |
| By eye | Stubby eight-sided cross-section |
| Scratch check | Knife scratches it with effort |
Anything that scratches, burns or dissolves the piece is a lab job. Get it appraised rather than testing it apart.
Care & handling.
At 5.5 to 6 on the Mohs scale it handles careful wear but scratches against quartz and dust. Store it separately and take rings off before rough work.
It breaks with two cleavages near 87°/93°; uneven fracture, which is worth knowing before you set it or drop it.
Warm water and a soft cloth clean almost everything. Ultrasonic tanks, steamers and household cleaners are where pieces get ruined.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)₂O₆. Crystal system: Monoclinic. Specific gravity: 3.2 to 3.6. Streak: Greenish gray. Cleavage and fracture: Two cleavages near 87°/93°; uneven fracture.
How it reaches the market
Basalts and gabbros worldwide; collectible loose crystals erode from volcanic ash in Italy (Vesuvius), Mexico, Oregon (USA).
What it gets confused with
Hornblende: Amphibole cleavages meet at 56°/124° and crystals are longer and shinier; augite's meet near 90° on stubbier blocks. Black tourmaline: Schorl is striated, glassy, with no cleavage. Diopside: Paler green pyroxene cousin, augite is the dark iron-rich field version.
What it is worth
Common; sharp loose crystals are inexpensive collector staples.
One more thing
Volcano flanks shed perfect little augite crystals after eruptions, rain washes them out of the ash like black confetti.
An education-first guide.
No product links here. We do not sell augite, and a guide that only covers our own shelves would not be much of a guide.
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