Sulfoborite is a rare magnesium borate-sulfate mineral that typically forms in evaporite deposits. Collectors value it for its delicate, acicular or prismatic crystal habits often found within salt dome environments.
Is this sulfoborite?
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 sulfoborite with a known reference. Sulfoborite sits at Mohs 4-4.5, 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: colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic to acicular crystals, often as radiating clusters or aggregates.
Often confused with
Sulfoborite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Sulfoborite is noticeably harder (Mohs 4-4.5 vs. 1.5-2); luster reads vitreous on Sulfoborite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
How to tell apart: Sulfoborite is noticeably harder (Mohs 4-4.5 vs. 2-2.5).
Often found alongside sulfoborite
Minerals reported to co-occur with sulfoborite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₃(SO₄)(B(OH)₄)₂·(OH,F)₂
- Mohs hardness
- 4-4.5
- Density
- 2.38-2.45 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic to acicular crystals, often as radiating clusters or aggregates
- Cleavage
- {110}, good; {001}, fair
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon mineral in marine salt deposits
Where rockhounds find sulfoborite
Classic worldwide localities
- Westeregeln, Saxony-Anhalt, and at the Wittmar potash mine, Asse, southwest of Braunschweig, Lower Saxony, Germany
- Forden, near Scarborough, Yorkshire, England
- Inder borate deposit, Kazakhstan
Field-hunting tip
Where it forms: An uncommon mineral in marine salt deposits. If you start seeing carnallite, anhydrite, boracite in float, you are in the right ground. Typical habit: prismatic to acicular crystals, often as radiating clusters or aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
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Find sulfoborite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
