Ferrobobfergusonite is a rare phosphate mineral found primarily within complex granite pegmatites. It typically occurs as part of a mineral series where iron replaces manganese, making it structurally related to the bobfergusonite-group species found in the Black Hills of South Dakota.
Is this ferrobobfergusonite?
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 ferrobobfergusonite with a known reference. Ferrobobfergusonite sits at Mohs ~5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale green-yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: deep green-brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: granular to prismatic crystals.
Often confused with
Ferrobobfergusonite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Ferrobobfergusonite is noticeably harder (Mohs ~5 vs. 4); streak differs, so Ferrobobfergusonite leaves pale green-yellow, Bobfergusonite leaves yellow-brown; luster reads vitreous on Ferrobobfergusonite and resinous, bronzy on parting planes on Bobfergusonite.
How to tell apart: Streak differs, so Ferrobobfergusonite leaves pale green-yellow, Triphylite leaves white to grayish white.
Often found alongside ferrobobfergusonite
Minerals reported to co-occur with ferrobobfergusonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂Fe²⁺₅Fe³⁺Al(PO₄)₆
- Mohs hardness
- ~5
- Density
- 3.68 g/cm³
- Colors
- Deep green-brown
- Streak
- Pale green-yellow
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Granular to prismatic crystals
- Cleavage
- Perfect on {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- granite pegmatites
Where rockhounds find ferrobobfergusonite
Classic worldwide localities
- Victory mine, Custer County, South Dakota, USA
Field-hunting tip
Where it forms: granite pegmatites. If you start seeing ferrowyllieite, schorl, fillowite in float, you are in the right ground. Typical habit: granular to prismatic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrobobfergusonite?+
Where is ferrobobfergusonite found?+
What rocks look like ferrobobfergusonite?+
What minerals are found with ferrobobfergusonite?+
What kind of rock does ferrobobfergusonite form in?+
What is ferrobobfergusonite used for?+
Find ferrobobfergusonite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
