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 vitreous to dull 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.
How to tell apart: Streak differs, so Gaudefroyite leaves brown, Braunite leaves black; luster reads vitreous to dull on Gaudefroyite and submetallic on Braunite.
How to tell apart: Streak differs, so Gaudefroyite leaves brown, Hausmannite leaves dark reddish brown; luster reads vitreous to dull on Gaudefroyite and submetallic on Hausmannite.
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
- Vitreous to Dull
- 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
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, 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
How do you identify gaudefroyite?+
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What rocks look like gaudefroyite?+
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Find gaudefroyite on the map
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