Delvauxite is a rare hydrated iron calcium phosphate mineral that typically forms as amorphous, waxy-looking botryoidal or reniform crusts. It is most often found in secondary alteration zones of phosphate-bearing rocks or weathered sedimentary deposits. Collectors prize it for its smooth, resinous appearance and distinct yellow-brown coloration.
Is this delvauxite?
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 delvauxite with a known reference. Delvauxite sits at Mohs 2.5-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Delvauxite leaves a yellowish streak.
- 3Read the lusterHold the specimen under a strong light. Delvauxite typically shows a resinous luster.
- 4Match the color rangeCompare against the expected color range: yellow, brown, reddish-brown, black.
- 5Look at form & habitCrystal system: amorphous. Typical habit: botryoidal, reniform, massive.
Often confused with
Delvauxite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Limonite is the harder of the two (Mohs 4-5.5 vs. 2.5-3); streak differs, so Delvauxite leaves yellowish, Limonite leaves yellowish-brown; luster reads resinous on Delvauxite and submetallic to earthy on Limonite.
How to tell apart: Streak differs, so Delvauxite leaves yellowish, Beraunite leaves brown; luster reads resinous on Delvauxite and vitreous on Beraunite.
Often found alongside delvauxite
Minerals reported to co-occur with delvauxite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaFe₄(PO₄,SO₄)₂(OH)₈·4-6H₂O
- Mohs hardness
- 2.5-3
- Density
- 2.0-2.3 g/cm³
- Streak
- Yellowish
- Luster
- Resinous
- Transparency
- Translucent
- Crystal system
- Amorphous
- Crystal habit
- Botryoidal, Reniform, Massive
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Sedimentary Deposits, Weathering Zones
- Typical price
- $20-100 per specimen
Where rockhounds find delvauxite
Classic worldwide localities
- Liège, Belgium
- Czech Republic
- Germany
- USA
Field-hunting tip
Look in sedimentary deposits, weathering zones country, the host setting where delvauxite typically forms. If you start seeing limonite, vivianite, strengite in float, you are in the right ground. Field specimens usually show a botryoidal, reniform, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find delvauxite on the map
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