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Hornblende
Hornblende is inosilicate (amphibole), Ca₂(Mg,Fe,Al)₅(Al,Si)₈O₂₂(OH)₂. In the hand, it rates 5 to 6 on the Mohs scale, and it runs black and greenish black. The everyday black mineral of speckled rocks, glossy stubby prisms with diamond-shaped cross-sections and oblique amphibole cleavage.
The geology.
Hornblende carries the formula Ca₂(Mg,Fe,Al)₅(Al,Si)₈O₂₂(OH)₂. It belongs to the monoclinic system. Catalogues list it as inosilicate (amphibole).
It sits at 5 to 6 on the Mohs scale. The surface reads vitreous to dull. Light behaviour is opaque. Specific gravity runs 3.0 to 3.4. The streak is gray to gray-green. It breaks with two perfect cleavages at ~56°/124°; splintery.
The everyday black mineral of speckled rocks, glossy stubby prisms with diamond-shaped cross-sections and oblique amphibole cleavage.
It reaches buyers as stubby prisms in granite and diorite, bladed masses or loose crystals from volcanic ash.
The origins.
Granites, diorites, amphibolites worldwide, among the commonest dark minerals of continental rock.
On value, the database notes: common and inexpensive.
Traditional associations.
In energy work traditions, hornblende has little shop lore; modern writers cast it as a temper-cooling grounding stone.
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.
The everyday black mineral of speckled rocks, glossy stubby prisms with diamond-shaped cross-sections and oblique amphibole cleavage.
| Looks like | How to tell them apart |
|---|---|
| Augite | The pyroxene rival, augite's cleavages meet near 90°, hornblende's at 56°/124°; augite's cross-section is squarer |
| Black tourmaline | Schorl is striated, glassy, with no cleavage at all |
| Biotite | Biotite peels into flexible sheets |
At-home tests.
Before anyone talks you into a lab report, these are the checks worth doing yourself on hornblende.
| Test | What you should see |
|---|---|
| By eye | Diamond (rhombic) cross-section on prisms |
| By eye | Oblique cleavage intersections |
| Scratch check | Knife scratches it with effort |
If these checks leave you unsure, that is what appraisers are for. Do not file, heat or soak a piece to find out.
Care & handling.
At 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 perfect cleavages at ~56°/124°; splintery, which is worth knowing before you set it or drop it.
Most damage happens during cleaning, not wearing. Avoid steamers, ultrasonic tanks and anything from under the sink.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is Ca₂(Mg,Fe,Al)₅(Al,Si)₈O₂₂(OH)₂. Crystal system: Monoclinic. Specific gravity: 3.0 to 3.4. Streak: Gray to gray-green. Cleavage and fracture: Two perfect cleavages at ~56°/124°; splintery.
How it reaches the market
Granites, diorites, amphibolites worldwide, among the commonest dark minerals of continental rock.
What it gets confused with
Augite: The pyroxene rival, augite's cleavages meet near 90°, hornblende's at 56°/124°; augite's cross-section is squarer. Black tourmaline: Schorl is striated, glassy, with no cleavage at all. Biotite: Biotite peels into flexible sheets.
What it is worth
Common and inexpensive.
One more thing
The name is old German miners' slang, 'horn' for its luster, 'blende' for 'deceiver', ore-looking rock that paid nothing.
An education-first guide.
There is nothing to buy on this page. Hornblende is not part of our catalogue, and the guide is here anyway because somebody searching the name deserves a straight answer.
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