Ferrinatrite is a rare sodium iron sulfate mineral that typically forms as an efflorescence in the oxidized zones of arid mining districts. It is highly soluble in water, meaning collectors must keep specimens in a dry environment to prevent dehydration or degradation.
Is this ferrinatrite?
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 ferrinatrite with a known reference. Ferrinatrite 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. Ferrinatrite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Ferrinatrite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: pale yellow, yellowish white, colorless.
- 5Look at form & habitCrystal system: trigonal. Typical habit: prismatic crystals, fibrous, crusts, efflorescent aggregates.
Often confused with
Ferrinatrite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Ferrinatrite leaves white, Copiapite leaves yellow; luster reads vitreous on Ferrinatrite and pearly on Copiapite.
How to tell apart: Luster reads vitreous on Ferrinatrite and silky on Fibroferrite.
Often found alongside ferrinatrite
Minerals reported to co-occur with ferrinatrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₃Fe(SO₄)₃·3H₂O
- Mohs hardness
- 2.5
- Density
- 2.55 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Prismatic Crystals, Fibrous, Crusts, Efflorescent Aggregates
- Cleavage
- Distinct On {1010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Sulfide Ore Deposits in Arid Climates
- Typical price
- $20-150 for small mineral specimens
Where rockhounds find ferrinatrite
Classic worldwide localities
- Chuquicamata, Chile
- Cerro Pintados, Chile
- Alcaparrosa Mine, Chile
- Antofagasta, Chile
Field-hunting tip
Look in oxidized zones of sulfide ore deposits in arid climates country — that is the host setting where ferrinatrite typically forms. If you start seeing coquimbite, copiapite, halotrichite in float, you are in the right ground. Field specimens usually show a prismatic crystals, fibrous, crusts, efflorescent aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find ferrinatrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
