Sturmanite is a rare boron-bearing sulfate typically found as vibrant yellow-orange hexagonal prisms in manganese mines. It is highly prized by collectors for its sharp crystal form and intense fluorescence under ultraviolet light.
Is this sturmanite?
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 sturmanite with a known reference. Sturmanite sits at Mohs ~2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale yellow, greenish yellow, brownish orange if altered.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, slightly greasy on fracture surfaces.
- 4Match the color rangeCompare against the expected color range: yellow, greenish yellow, yellow green, orange brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: hexagonal, prismatic, pyramidal.
Often confused with
Sturmanite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Sturmanite leaves pale yellow, greenish yellow, brownish orange if altered, Ettringite leaves white.
How to tell apart: Thaumasite is the harder of the two (Mohs 3.5 vs. ~2.5); streak differs, so Sturmanite leaves pale yellow, greenish yellow, brownish orange if altered, Thaumasite leaves white.
Often found alongside sturmanite
Minerals reported to co-occur with sturmanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₆Fe₂(SO₄)₂.₅[B(OH)₄](OH)₁₂·25H₂O
- Mohs hardness
- ~2.5
- Density
- 1.847 g/cm³
- Streak
- Pale yellow, greenish yellow, brownish orange if altered
- Luster
- Vitreous, slightly greasy on fracture surfaces
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
- Crystal habit
- Hexagonal, prismatic, pyramidal
- Cleavage
- On {1010}, perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon secondary mineral in cavities in metamorphosed bedded manganese deposits
Where rockhounds find sturmanite
Classic worldwide localities
- Kuruman district, Wessels and N’Chwaning II mines, Cape Province, South Africa
Field-hunting tip
Where it forms: An uncommon secondary mineral in cavities in metamorphosed bedded manganese deposits. If you start seeing barite, manganite, hausmannite in float, you are in the right ground. Typical habit: hexagonal, prismatic, pyramidal. Train your eye for that shape before scanning the outcrop.
Common questions
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Find sturmanite on the map
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