Ferrohexahydrite is a rare secondary sulfate mineral that typically forms as a dehydration product of melanterite in oxidized iron-rich environments. Collectors will primarily find it as pale green to white efflorescent crusts or powdery aggregates, often requiring careful storage as it is highly unstable in humid conditions.
Is this ferrohexahydrite?
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 ferrohexahydrite with a known reference. Ferrohexahydrite 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: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive, granular, or crusts.
Often confused with
Ferrohexahydrite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside ferrohexahydrite
Minerals reported to co-occur with ferrohexahydrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- FeSO₄·6H₂O
- Mohs hardness
- 2
- Density
- 1.934 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Massive, granular, or crusts
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In oxidized ore-bearing sandstone (Sofiya mine, Ukraine); a dehydration product of melanterite in drill cores (northeastern Tatarstan, Russia)
Where rockhounds find ferrohexahydrite
Classic worldwide localities
- Found along Contrary Creek, Louisa Co., Virginia, USA
- Sofiya mine, Nikitovka mercury deposit, Gorlovka, Ukraine
- Olkusz, northwest of Krakow, Poland
- An unspecified locality in northeastern Tatarstan, Russia
- Jáchymov (Joachimsthal), Czech Republic
- Vesuvius, Campania, and from the Conchea mine, near Rio Marina, Elba, Italy
Field-hunting tip
Where it forms: In oxidized ore-bearing sandstone (Sofiya mine, Ukraine); a dehydration product of melanterite in drill cores (northeastern Tatarstan, Russia). If you start seeing melanterite in float, you are in the right ground. Typical habit: massive, granular, or crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify ferrohexahydrite?+
Where is ferrohexahydrite found?+
What rocks look like ferrohexahydrite?+
What minerals are found with ferrohexahydrite?+
What kind of rock does ferrohexahydrite form in?+
What is ferrohexahydrite used for?+
Find ferrohexahydrite on the map
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