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 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: colorless, yellowish, white, green, red.
- 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
- 4
- Density
- 2.53 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Prismatic crystals, radial aggregates
- Cleavage
- {010}, perfect; {100}, poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In sedimentary phosphatic nodules (Fairfield, Utah, USA); a late mineral in highly oxidized phosphate nodules in granite pegmatite (South Dakota, USA)
Where rockhounds find montgomeryite
Classic worldwide localities
- Little Green Monster mine, Clay Canyon, about nine km west of Fairfield, Utah Co., USA
- Etta mine, near Keystone, Pennington Co., and at the Tip Top mine, 8.5 km southwest of Custer, Custer Co., South Dakota, USA
- Redhouse Barite mine, Golconda district, Humboldt Co., Nevada, USA
- Lavra da Ilha pegmatite, in the Jequitinhonha River, three km north of Taquaral, Minas Gerais, Brazil
- Iron Monarch quarry, Iron Knob, and the Moculta phosphate quarry, northeast of Angaston, South Australia
- Mangualde pegmatite, near Mesquitela, and the Bendada pegmatite, near Guarda, Portugal
Field-hunting tip
Where it forms: In sedimentary phosphatic nodules (Fairfield, Utah, USA); a late mineral in highly oxidized phosphate nodules in granite pegmatite (South Dakota, USA). If you start seeing variscite, englishite, wardite in float, you are in the right ground. Typical habit: prismatic crystals, radial aggregates. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify montgomeryite?+
Where is montgomeryite found?+
What rocks look like montgomeryite?+
What minerals are found with montgomeryite?+
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What is montgomeryite used for?+
Find montgomeryite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
