Koninckite is a rare hydrated iron phosphate that typically forms as small radiating clusters or earthy crusts within iron-rich sedimentary deposits. It is frequently found as an alteration product in association with goethite or limonite. Collectors prize it for its delicate, needle-like formations and vibrant yellow coloration.
Is this koninckite?
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 koninckite with a known reference. Koninckite 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 yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: yellow, white.
- 5Look at form & habitCrystal system: tetragonal. Typical habit: aggregates, spherical.
Often confused with
Koninckite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Koninckite leaves pale yellow, Strengite leaves white.
How to tell apart: Koninckite is noticeably harder (Mohs 3.5 vs. 1.5-2); streak differs, so Koninckite leaves pale yellow, Vivianite leaves white, altering to dark blue, brown.
How to tell apart: Variscite is the harder of the two (Mohs 4.5 vs. 3.5); streak differs, so Koninckite leaves pale yellow, Variscite leaves white.
Often found alongside koninckite
Minerals reported to co-occur with koninckite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FePO₄·3H₂O
- Mohs hardness
- 3.5
- Density
- 2.40 g/cm³
- Streak
- Pale yellow
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Tetragonal
- Crystal habit
- Aggregates, spherical
- Cleavage
- One, transverse to elongation
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Presumably as a secondary mineral in phosphatic sedimentary rocks (Richelle, Belgium); in a hydrothermally altered andesite enriched in Fe, SO4, and PO4 (Suwa mine, Japan)
Where rockhounds find koninckite
Classic worldwide localities
- Richelle, near Visé, Belgium
- A cave near Oni-Ana, Fukushima Prefecture, and at the Suwa mine, about seven km south-southwest of Mt. Tateshina, Nagano Prefecture, Japan
- Kovdor massif, Kola Peninsula, Russia
Field-hunting tip
Where it forms: Presumably as a secondary mineral in phosphatic sedimentary rocks (Richelle, Belgium); in a hydrothermally altered andesite enriched in Fe, SO4, and PO4 (Suwa mine, Japan). If you start seeing richellite, halloysite, allophane in float, you are in the right ground. Typical habit: aggregates, spherical. Train your eye for that shape before scanning the outcrop.
Common questions
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Find koninckite on the map
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