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 ~3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: pale brown.
- 3Read the lusterHold the specimen under a strong light. Luster: waxy to opaline.
- 4Match the color rangeCompare against the expected color range: yellowish brown, brown, reddish brown, brownish black.
- 5Look at form & habitCrystal system: amorphous. Typical habit: amorphous, concretionary, stalactitic.
Often confused with
Delvauxite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Delvauxite leaves pale brown, Limonite leaves yellowish-brown; luster reads waxy to opaline on Delvauxite and submetallic to earthy on Limonite.
How to tell apart: Streak differs, so Delvauxite leaves pale brown, Beraunite leaves olive-drab when fresh; yellow, brownish yellow on exposure; luster reads waxy to opaline on Delvauxite and vitreous, pearly on cleavages, resinous on fractures 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)₂(OH)₈·4-5H₂O
- Mohs hardness
- ~3.5
- Density
- 2.377-2.530 g/cm³
- Streak
- Pale brown
- Luster
- Waxy to opaline
- Transparency
- Opaque to translucent
- Crystal system
- Amorphous
- Crystal habit
- Amorphous, concretionary, stalactitic
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In gossan (Nenačovice, Czech Republic)
Where rockhounds find delvauxite
Classic worldwide localities
- Berneau, Richelle, and Argenteau, all near Visé, Belgium
- Tollinggraben, Leoben, Styria, Austria
- Nenačovice and Trubín, Czech Republic
- Železník (Vashegy), Slovakia
- Fouchères, Aube, France
- St. John’s quarry, near Kapunda, Mount Lofty Ranges, South Australia
Field-hunting tip
Where it forms: In gossan (Nenačovice, Czech Republic). If you start seeing diadochite, vivianite, pitticite in float, you are in the right ground. Typical habit: amorphous, concretionary, stalactitic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify delvauxite?+
Where is delvauxite found?+
What rocks look like delvauxite?+
What minerals are found with delvauxite?+
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Find delvauxite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
