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, so Bournonite leaves steel-gray, Galena leaves lead-gray.
How to tell apart: Streak differs, so Bournonite leaves steel-gray, Tetrahedrite leaves black.
How to tell apart: Streak differs, so 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, 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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