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 — Delvauxite leaves yellowish, Limonite leaves yellowish-brown; luster reads resinous on Delvauxite and submetallic to earthy on Limonite.
How to tell apart: Streak differs — 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 — that is 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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