Gaudefroyite is a rare manganese borate mineral known primarily from the Kalahari Manganese Fields. It typically forms sharp, striated hexagonal prismatic crystals with a distinct submetallic luster, usually occurring in complex mineralized vugs.
Is this gaudefroyite?
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 gaudefroyite with a known reference. Gaudefroyite sits at Mohs 5.5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Gaudefroyite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Gaudefroyite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: black, brownish-black.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: prismatic crystals, sometimes in radiating clusters.
Often confused with
Gaudefroyite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside gaudefroyite
Minerals reported to co-occur with gaudefroyite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄Mn₃(BO₃)₃(CO₃)O
- Mohs hardness
- 5.5-6
- Density
- 3.48 g/cm³
- Colors
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Prismatic Crystals, Sometimes in Radiating Clusters
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Manganiferous Hydrothermal Veins in Sedimentary Deposits
- Typical price
- $50-500 depending on crystal size and matrix quality
Where rockhounds find gaudefroyite
Classic worldwide localities
- N'Chwaning Mines, Kalahari Manganese Fields, South Africa
Field-hunting tip
Look in manganiferous hydrothermal veins in sedimentary deposits country — that is the host setting where gaudefroyite typically forms. If you start seeing calcite, andradite, baryte in float, you are in the right ground. Field specimens usually show a prismatic crystals, sometimes in radiating clusters habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find gaudefroyite on the map
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