Fibroferrite is a hydrated iron sulfate that typically forms delicate, silky, fibrous masses or radiating acicular sprays. It is a secondary mineral found in the oxidation zones of iron-rich sulfide ore bodies, often occurring as an efflorescence in arid mining districts.
Is this fibroferrite?
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 fibroferrite with a known reference. Fibroferrite sits at Mohs 2.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Fibroferrite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Fibroferrite typically shows a silky luster.
- 4Match the color rangeCompare against the expected color range: yellow, white, greenish-yellow, pale orange.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, acicular, radiating, globular.
Often confused with
Fibroferrite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Fibroferrite leaves white, Copiapite leaves yellow; luster reads silky on Fibroferrite and pearly on Copiapite.
How to tell apart: Luster reads silky on Fibroferrite and vitreous on Halotrichite.
How to tell apart: Luster reads silky on Fibroferrite and vitreous on Melanterite.
Often found alongside fibroferrite
Minerals reported to co-occur with fibroferrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe³⁺(SO₄)(OH)·5H₂O
- Mohs hardness
- 2.5
- Density
- 2.2-2.3 g/cm³
- Streak
- White
- Luster
- Silky
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, Acicular, Radiating, Globular
- Cleavage
- Perfect
- Rarity
- Uncommon
- Uses
- Collector
- Host rock
- Oxidized Zones of Sulfide Ore Deposits
- Typical price
- $10-60 per specimen
Where rockhounds find fibroferrite
Classic worldwide localities
- Chuquicamata, Chile
- Rio Tinto, Spain
- Cerro de Pasco, Peru
- Alcaparrosa mine, Chile
Field-hunting tip
Look in oxidized zones of sulfide ore deposits country — that is the host setting where fibroferrite typically forms. If you start seeing jarosite, copiapite, coquimbite in float, you are in the right ground. Field specimens usually show a fibrous, acicular, radiating, globular habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find fibroferrite on the map
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