Stewartite is a rare phosphate mineral often found as an alteration product of triphylite in phosphate-rich pegmatites. It typically appears as orange, fibrous, or bladed crystal aggregates and is highly sought after by systematic mineral collectors.
Is this stewartite?
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 stewartite with a known reference. Stewartite sits at Mohs 1.5-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Stewartite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Stewartite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: orange, reddish-orange, brownish-orange.
- 5Look at form & habitCrystal system: triclinic. Typical habit: bladed, fibrous aggregates, crusts.
Often confused with
Stewartite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside stewartite
Minerals reported to co-occur with stewartite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn²⁺Fe³⁺₂(PO₄)₂(OH)₂·8H₂O
- Mohs hardness
- 1.5-2
- Density
- 2.44 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Triclinic
- Crystal habit
- Bladed, Fibrous Aggregates, Crusts
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
- Typical price
- $20-150 for micro-mounts or small specimens
Where rockhounds find stewartite
Classic worldwide localities
- Stewart Mine, Pala, California, USA
- Hagendorf-Pleystein, Bavaria, Germany
- Mangualde, Viseu, Portugal
- Sapucaia Mine, Minas Gerais, Brazil
Field-hunting tip
Look in granite pegmatites country, the host setting where stewartite typically forms. If you start seeing sicklerite, triphylite, hureaulite in float, you are in the right ground. Field specimens usually show a bladed, fibrous aggregates, crusts habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find stewartite on the map
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