Fillowite is a rare phosphate mineral typically found as granular or massive aggregates in complex granite pegmatites. It is often identified by its yellowish-brown color and vitreous luster, frequently occurring alongside other rare phosphate minerals in pockets. Collectors prize it as a significant, though obscure, member of the phosphate-rich zones in pegmatites.
Is this fillowite?
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 fillowite with a known reference. Fillowite sits at Mohs 4.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Fillowite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Fillowite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: yellowish-brown, reddish-brown, yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: granular, massive, rarely in rhombohedral crystals.
Often confused with
Fillowite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside fillowite
Minerals reported to co-occur with fillowite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₂CaMn₇(PO₄)₆
- Mohs hardness
- 4.5
- Density
- 3.42 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Granular, Massive, Rarely in Rhombohedral Crystals
- Cleavage
- Perfect On {0001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
- Typical price
- $20-150 for small specimens
Where rockhounds find fillowite
Classic worldwide localities
- Branchville, Connecticut, USA
- Keystone, South Dakota, USA
- Mangualde, Portugal
- Hagendorf, Germany
Field-hunting tip
Look in granite pegmatites country — that is the host setting where fillowite typically forms. If you start seeing apatite, triphylite, hureaulite in float, you are in the right ground. Field specimens usually show a granular, massive, rarely in rhombohedral crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find fillowite on the map
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