Bournonite is highly prized by collectors for its unique cyclic twinning that forms distinctive wheel-shaped crystals, earning it the nickname 'cogwheel ore.' It is a lead-copper-antimony sulfide typically found in hydrothermal vein deposits alongside other metallic sulfides.
Is this bournonite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch bournonite with a known reference. Bournonite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Bournonite leaves a steel-gray streak.
- 3Read the lusterHold the specimen under a strong light. Bournonite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: steel-gray, iron-black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, often showing cyclic twinning resulting in cogwheel-like shapes.
Often confused with
Bournonite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Bournonite leaves steel-gray, Galena leaves lead-gray.
How to tell apart: Streak differs — Bournonite leaves steel-gray, Tetrahedrite leaves black.
How to tell apart: Streak differs — Bournonite leaves steel-gray, Jamesonite leaves gray-black.
Often found alongside bournonite
Minerals reported to co-occur with bournonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- PbCuSbS₃
- Mohs hardness
- 2.5-3
- Density
- 5.7-5.9 g/cm³
- Colors
- Streak
- Steel-gray
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Often Showing Cyclic Twinning Resulting in Cogwheel-like Shapes
- Cleavage
- Imperfect On {010}
- Rarity
- Uncommon
- Uses
- Collector, Mineralogical Study
- Host rock
- Hydrothermal Veins
- Typical price
- $20-150 thumbnail, $200-2000 cabinet specimen
Where rockhounds find bournonite
Classic worldwide localities
- Les Malines, France
- Herodsfoot Mine, Cornwall, UK
- Casapalca, Peru
- Oruro, Bolivia
- Doi Pui, Thailand
Field-hunting tip
Look in hydrothermal veins country — that is the host setting where bournonite typically forms. If you start seeing galena, tetrahedrite, pyrite in float, you are in the right ground. Field specimens usually show a tabular crystals, often showing cyclic twinning resulting in cogwheel-like shapes habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find bournonite on the map
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