Ferrorockbridgeite is a rare phosphate mineral typically found as an alteration product of triphylite in complex granitic pegmatites. Collectors look for its characteristic dark, radiating fibrous or botryoidal crusts often associated with secondary phosphate assemblages.
Is this ferrorockbridgeite?
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 ferrorockbridgeite with a known reference. Ferrorockbridgeite sits at Mohs 4.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Ferrorockbridgeite leaves a brownish green streak.
- 3Read the lusterHold the specimen under a strong light. Ferrorockbridgeite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dark brown, black, greenish black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, radiating, botryoidal, massive.
Often confused with
Ferrorockbridgeite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside ferrorockbridgeite
Minerals reported to co-occur with ferrorockbridgeite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Fe²⁺,Mn²⁺)Fe³⁺₄(PO₄)₃(OH)₅
- Mohs hardness
- 4.5
- Density
- 3.8-3.9 g/cm³
- Streak
- Brownish Green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Radiating, Botryoidal, Massive
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector, Mineralogical Study
- Host rock
- Granite Pegmatites
- Typical price
- $20-150 for micromounts and thumbnails
Where rockhounds find ferrorockbridgeite
Classic worldwide localities
- Hagendorf, Germany
- Tip Top Mine, South Dakota, USA
- Nickel Plate Mine, South Dakota, USA
- Dawson, Yukon, Canada
Field-hunting tip
Look in granite pegmatites country — that is the host setting where ferrorockbridgeite typically forms. If you start seeing triphylite, vivianite, strengite in float, you are in the right ground. Field specimens usually show a fibrous, radiating, botryoidal, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferrorockbridgeite on the map
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