Congolite is a rare member of the boracite group typically found in salt dome environments. Collectors should look for its distinctive pseudo-cubic trigonal crystals, which are frequently associated with potash-bearing evaporite sequences.
Is this congolite?
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 congolite with a known reference. Congolite sits at Mohs 7, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: light red.
- 5Look at form & habitCrystal system: trigonal. Typical habit: equant pseudo-cubic crystals, massive.
Often confused with
Congolite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside congolite
Minerals reported to co-occur with congolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₃B₇O₁₃Cl
- Mohs hardness
- 7
- Density
- 3.58 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Equant pseudo-cubic crystals, massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Part of insoluble residue from a drill core into sedimentary evaporites (Brazzaville, Congo); in a marine evaporite deposit (Penobsquis mine, Canada)
Where rockhounds find congolite
Classic worldwide localities
- Brazzaville, Congo
- Penobsquis evaporite deposit, near Sussex, New Brunswick, Canada
- Bischofferode, Thuringia, Germany
Field-hunting tip
Where it forms: Part of insoluble residue from a drill core into sedimentary evaporites (Brazzaville, Congo); in a marine evaporite deposit (Penobsquis mine, Canada). If you start seeing anhydrite, halite in float, you are in the right ground. Typical habit: equant pseudo-cubic crystals, massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify congolite?+
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What rocks look like congolite?+
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Find congolite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
