Montgomeryite is a rare phosphate mineral often found as small, clear, prismatic crystals within phosphate nodules. It is prized by micromount collectors for its aesthetic, well-formed terminations and is most famously associated with the variscite deposits of Fairfield, Utah.
Is this montgomeryite?
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 montgomeryite with a known reference. Montgomeryite sits at Mohs 3 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Montgomeryite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Montgomeryite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: prismatic crystals, radial aggregates.
Often confused with
Montgomeryite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside montgomeryite
Minerals reported to co-occur with montgomeryite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₄MgAl₄(PO₄)₆(OH)₄·12H₂O
- Mohs hardness
- 3
- Density
- 2.66 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic Crystals, Radial Aggregates
- Cleavage
- Perfect On {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Phosphate Nodules in Metamorphic Rocks and Clay-rich Sedimentary Deposits
- Typical price
- $20-200 thumbnail
Where rockhounds find montgomeryite
Classic worldwide localities
- Fairfield, Utah, USA
- Rapid Creek, Yukon, Canada
- Tip Top mine, South Dakota, USA
Field-hunting tip
Look in phosphate nodules in metamorphic rocks and clay-rich sedimentary deposits country — that is the host setting where montgomeryite typically forms. If you start seeing wardite, variscite, gordonite in float, you are in the right ground. Field specimens usually show a prismatic crystals, radial aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find montgomeryite on the map
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