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 3, 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: orange, brownish yellow, yellow.
- 5Look at form & habitCrystal system: triclinic. Typical habit: cryptocrystalline, fibrous.
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
- 3
- Density
- 2.94 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Semitransparent
- Crystal system
- Triclinic
- Crystal habit
- Cryptocrystalline, fibrous
- Cleavage
- Good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare oxidation product formed by the leaching of primary phosphates in complex zoned granite pegmatites
Where rockhounds find stewartite
Classic worldwide localities
- Stewart mine, Pala, San Diego Co., California, USA
- Palermo #1 and Fletcher mines, near North Groton, Grafton Co., New Hampshire, USA
- Newry, Oxford Co., Maine, USA
- Hesnard mine, three km southwest of Keystone, Pennington Co., and the Linwood, Tip Top, and White Elephant mines, near Custer, Custer Co., South Dakota, USA
- Boqueirão pegmatite, three km southeast of Parelhas, Rio Grande do Norte, Brazil
- Okatjimukuju pegmatite, near Karibib, Namibia
Field-hunting tip
Where it forms: A rare oxidation product formed by the leaching of primary phosphates in complex zoned granite pegmatites. If you start seeing lithiophilite, triphylite, huréaulite in float, you are in the right ground. Typical habit: cryptocrystalline, fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify stewartite?+
Where is stewartite found?+
What rocks look like stewartite?+
What minerals are found with stewartite?+
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What is stewartite used for?+
Find stewartite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
