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 6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to dull.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: prismatic.
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 brownish black to steel-gray; 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)O₃
- Mohs hardness
- 6
- Density
- 3.35-3.50 g/cm³
- Colors
- Streak
- Brown
- Luster
- Vitreous to dull
- Transparency
- Opaque, transparent in thin slivers
- Crystal system
- Hexagonal
- Crystal habit
- Prismatic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon hydrothermal mineral in manganese deposits
Where rockhounds find gaudefroyite
Classic worldwide localities
- Tachgagalt, 17 km south-southwest of Ouarzazate, Anti-Atlas Mountains, Morocco
- Wessels and N’Chwaning mines, near Kuruman, Cape Province, South Africa
Field-hunting tip
Where it forms: An uncommon hydrothermal mineral in manganese deposits. If you start seeing marokite, braunite, hausmannite in float, you are in the right ground. Typical habit: prismatic. 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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