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, so 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, 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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