Magnanelliite is a rare potassium iron sulfate mineral first discovered as a fumarolic sublimate at the La Fossa crater on Vulcano island. It typically forms as thin, platy, dark-colored crystals associated with other sulfate minerals in volcanic vent environments.
Is this magnanelliite?
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 magnanelliite with a known reference. Magnanelliite sits at Mohs 3.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Magnanelliite leaves a brown streak.
- 3Read the lusterHold the specimen under a strong light. Magnanelliite typically shows a submetallic luster.
- 4Match the color rangeCompare against the expected color range: dark brown, black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals.
Often confused with
Magnanelliite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Streak differs — Magnanelliite leaves brown, Römerite leaves yellow; luster reads submetallic on Magnanelliite and vitreous on Römerite.
How to tell apart: Streak differs — Magnanelliite leaves brown, Copiapite leaves yellow; luster reads submetallic on Magnanelliite and pearly on Copiapite.
Often found alongside magnanelliite
Minerals reported to co-occur with magnanelliite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₃Fe³⁺₂(SO₄)₄(OH)·2H₂O
- Mohs hardness
- 3.5
- Density
- 3.61 g/cm³
- Colors
- Streak
- Brown
- Luster
- Submetallic
- Transparency
- Opaque
- Crystal system
- Monoclinic
- Crystal habit
- Platy Crystals
- Cleavage
- Perfect On {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Fumarolic Sublimates
- Typical price
- n/a
Where rockhounds find magnanelliite
Classic worldwide localities
- La Fossa crater, Vulcano, Aeolian Islands, Italy
Field-hunting tip
Look in fumarolic sublimates country — that is the host setting where magnanelliite typically forms. If you start seeing alunogen, metavoltine, goldichite in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find magnanelliite on the map
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