Francisite is an incredibly rare copper bismuth selenite chloride mineral known primarily from the Centenario Mine in Bolivia. It typically forms attractive, small, green to blue-green platy crystals within oxidized ore zones. Collectors value it for its unusual composition and strictly limited locality occurrences.
Is this francisite?
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 francisite with a known reference. Francisite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale apple-green.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: light green.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: platy crystals, crusts.
Often confused with
Francisite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Francisite leaves pale apple-green, Chalcomenite leaves light blue; luster reads adamantine on Francisite and vitreous on Chalcomenite.
How to tell apart: Streak differs, so Francisite leaves pale apple-green, Penfieldite leaves white.
Often found alongside francisite
Minerals reported to co-occur with francisite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Cu₃Bi(SeO₃)₂O₂Cl
- Mohs hardness
- 3-4
- Density
- 5.42 g/cm³
- Colors
- Streak
- Pale apple-green
- Luster
- Adamantine
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Platy crystals, crusts
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in an oxidized barite lens in Precambrian sedimentary iron formation
Where rockhounds find francisite
Classic worldwide localities
- Iron Monarch quarry, Iron Knob, South Australia
- Baccu Locci mine, near Villaputzu, Sarrabus district, Sardinia, Italy
Field-hunting tip
Where it forms: A rare secondary mineral in an oxidized barite lens in Precambrian sedimentary iron formation. If you start seeing chorargyrite, muscovite, naumannite in float, you are in the right ground. Typical habit: platy crystals, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
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Find francisite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
