Bobfergusonite is a rare phosphate mineral typically found in phosphate nodules within iron-rich sedimentary formations. It is characterized by its distinct reddish-brown color and vitreous luster, often appearing as granular masses in mineral assemblages alongside other phosphates like ludlamite and vivianite.
Is this bobfergusonite?
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 bobfergusonite with a known reference. Bobfergusonite 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: yellow-brown.
- 3Read the lusterHold the specimen under a strong light. Luster: resinous, bronzy on parting planes.
- 4Match the color rangeCompare against the expected color range: reddish brown, greenish brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: granular to massive.
Often confused with
Bobfergusonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Bobfergusonite leaves yellow-brown, Fillowite leaves white; luster reads resinous, bronzy on parting planes on Bobfergusonite and subresinous to greasy on Fillowite.
How to tell apart: Triplite is the harder of the two (Mohs 5-5.5 vs. 4); streak differs, so Bobfergusonite leaves yellow-brown, Triplite leaves white to brown; luster reads resinous, bronzy on parting planes on Bobfergusonite and vitreous to resinous on Triplite.
Often found alongside bobfergusonite
Minerals reported to co-occur with bobfergusonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Mn²⁺₅Fe³⁺Al(PO₄)₆
- Mohs hardness
- 4
- Density
- 3.54 g/cm³
- Streak
- Yellow-brown
- Luster
- Resinous, bronzy on parting planes
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Granular to massive
- Cleavage
- On {010}, perfect; a parting on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon primary mineral in the intermediate zone of a granite pegmatite enriched in manganese and fluorine
Where rockhounds find bobfergusonite
Classic worldwide localities
- Gotcha claim, on an island in Cross Lake, Manitoba, Canada
Field-hunting tip
Where it forms: An uncommon primary mineral in the intermediate zone of a granite pegmatite enriched in manganese and fluorine. If you start seeing beusite, fillowite, triplite in float, you are in the right ground. Typical habit: granular to massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find bobfergusonite on the map
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