Seamanite is a very rare manganese phosphate-borate mineral primarily found in the iron mines of Michigan. It typically occurs as small, delicate, yellow to brownish prismatic crystals associated with other manganese minerals.
Is this seamanite?
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 seamanite with a known reference. Seamanite sits at Mohs 4, 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: yellow, yellow brown, light pink, wine yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular.
Often confused with
Seamanite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside seamanite
Minerals reported to co-occur with seamanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₃B(PO₄)(OH)₆
- Mohs hardness
- 4
- Density
- 3.08-3.128 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular
- Cleavage
- On {001}, distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In fractures cutting siliceous rock
Where rockhounds find seamanite
Classic worldwide localities
- Chicagoan mine, near Iron River, Iron Co., Michigan, USA
Field-hunting tip
Where it forms: In fractures cutting siliceous rock. If you start seeing sussexite, calcite, manganese oxide in float, you are in the right ground. Typical habit: acicular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify seamanite?+
Where is seamanite found?+
What rocks look like seamanite?+
What minerals are found with seamanite?+
What kind of rock does seamanite form in?+
What is seamanite used for?+
Find seamanite on the map
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