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, 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
How do you identify fillowite?+
Where is fillowite found?+
How much is fillowite worth?+
What rocks look like fillowite?+
What minerals are found with fillowite?+
What kind of rock does fillowite form in?+
What is fillowite used for?+
Find fillowite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
