Feroxyhyte is a rare iron oxyhydroxide polymorph that typically forms as an unstable, fine-grained precipitate in marine environments or oxidation zones. It is rarely found as well-developed crystals, appearing instead as thin coatings, nodules, or earthy masses. Collectors prize it primarily for its occurrence in ferromanganese nodules from deep-sea settings.
Is this feroxyhyte?
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 feroxyhyte with a known reference. Feroxyhyte sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: brown.
- 5Look at form & habitCrystal system: hexagonal. Typical habit: concretionary, massive, nodular.
Often confused with
Feroxyhyte vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Goethite is the harder of the two (Mohs 5-5.5 vs. 2); streak differs, so Feroxyhyte leaves yellow, Goethite leaves brownish yellow, yellow-orange, ocher-yellow; luster reads dull on Feroxyhyte and imperfect adamantine metallic to dull earthy; silky when fibrous on Goethite.
How to tell apart: Lepidocrocite is the harder of the two (Mohs 5 vs. 2); streak differs, so Feroxyhyte leaves yellow, Lepidocrocite leaves dull orange; luster reads dull on Feroxyhyte and submetallic on Lepidocrocite.
How to tell apart: Hematite is the harder of the two (Mohs 5-6 vs. 2); streak differs, so Feroxyhyte leaves yellow, Hematite leaves cherry-red or reddish brown; luster reads dull on Feroxyhyte and metallic or submetallic to dull on Hematite.
Often found alongside feroxyhyte
Minerals reported to co-occur with feroxyhyte. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeO(OH)
- Mohs hardness
- 2
- Density
- 4.2 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Dull
- Transparency
- Opaque
- Crystal system
- Hexagonal
- Crystal habit
- Concretionary, massive, nodular
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- In sea-floor Fe–Mn concretions
Where rockhounds find feroxyhyte
Classic worldwide localities
- Soils around Kolomyya, Carpathian Mountains, Ukraine
- Moscow, Ryazan, and Smolensk, Russia
- Floors of the Pacific Ocean, at depths of 4800 m, and the Baltic, White, and Kara Seas
- Found in the Koktenkol deposit, central Kazakhstan
- Holocene sediments near Parainen and Somero, Finland
- Laurium, Greece, in slag
Field-hunting tip
Where it forms: In sea-floor Fe–Mn concretions. If you start seeing lepidocrocite, goethite in float, you are in the right ground. Typical habit: concretionary, massive, nodular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify feroxyhyte?+
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Find feroxyhyte on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
