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Tennantite
Tennantite is sulfosalts (tetrahedrite group), Cu12As4S13. In the hand, it rates 3.5 to 4 on the Mohs scale, and it runs steel gray and iron black. Steel-gray metallic tetrahedra (four-faced pyramid shapes), the arsenic end of the fahlore family, slightly lighter in heft than its antimony twin tetrahedrite.
The geology.
Tennantite carries the formula Cu12As4S13. It belongs to the isometric system. Catalogues list it as sulfosalts (tetrahedrite group).
It sits at 3.5 to 4 on the Mohs scale. The surface reads metallic. Light behaviour is opaque. Specific gravity runs 4.6 to 4.7. The streak is black to reddish gray. It breaks with no cleavage; uneven to subconchoidal fracture.
Steel-gray metallic tetrahedra (four-faced pyramid shapes), the arsenic end of the fahlore family, slightly lighter in heft than its antimony twin tetrahedrite.
It reaches buyers as tetrahedral crystals, massive ore or crystals with quartz and pyrite.
The origins.
Copper veins and porphyry systems: Tsumeb (Namibia), Butte (Montana, USA), Cornwall (England), Peru.
On value, the database notes: collector mineral; sharp Tsumeb tetrahedra are classics.
Traditional associations.
In energy work traditions, associated with shielding and steady practical focus.
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.
Steel-gray metallic tetrahedra (four-faced pyramid shapes), the arsenic end of the fahlore family, slightly lighter in heft than its antimony twin tetrahedrite.
Not faked; tennantite/tetrahedrite labels are interchangeable guesses without analysis, buy by specimen quality.
| Looks like | How to tell them apart |
|---|---|
| Tetrahedrite | Visually near-identical; tetrahedrite (Sb) is denser (4.9 to 5.1), analysis or locality knowledge separates them |
| Sphalerite (dark) | Sphalerite shows resinous luster on cleavage flashes and pale streak |
| Magnetite | Magnetite is strongly magnetic and forms octahedra, not tetrahedra |
At-home tests.
Before anyone talks you into a lab report, these are the checks worth doing yourself on tennantite.
| Test | What you should see |
|---|---|
| By eye | Tetrahedral crystal form |
| Magnet check | Non-magnetic, no cleavage |
| By eye | SG noticeably under tetrahedrite when measurable |
Destructive tests belong to a gemologist, not a kitchen table. If a piece matters to you, pay for an appraisal before you take a file to it.
Care & handling.
At 3.5 to 4 on the Mohs scale this is a soft material. Keep it as a display piece, store it apart from harder stones, and skip daily-wear settings.
It breaks with no cleavage; uneven to subconchoidal fracture, which is worth knowing before you set it or drop it.
Clean it by hand, dry it properly, and keep it away from ultrasonic cleaners and hot steam.
Arsenic-bearing sulfosalt: wash hands after handling, avoid dust, no elixirs.
A deeper look.
Extended detail on composition, sourcing, authentication and market value.
The physical record
The formula on record is Cu12As4S13. Crystal system: Isometric. Specific gravity: 4.6 to 4.7. Streak: Black to reddish gray. Cleavage and fracture: No cleavage; uneven to subconchoidal fracture.
How it reaches the market
Copper veins and porphyry systems: Tsumeb (Namibia), Butte (Montana, USA), Cornwall (England), Peru.
What it gets confused with
Tetrahedrite: Visually near-identical; tetrahedrite (Sb) is denser (4.9 to 5.1), analysis or locality knowledge separates them. Sphalerite (dark): Sphalerite shows resinous luster on cleavage flashes and pale streak. Magnetite: Magnetite is strongly magnetic and forms octahedra, not tetrahedra.
What it is worth
Collector mineral; sharp Tsumeb tetrahedra are classics.
Where buyers get caught
Not faked; tennantite/tetrahedrite labels are interchangeable guesses without analysis, buy by specimen quality.
One more thing
Fahlores like tennantite are copper ore with a sting, smelters charge penalties for the arsenic that Victorian Cornish miners breathed daily.
An education-first guide.
We do not stock tennantite. Writing it up regardless is the point of a reference library.
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