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, so Magnanelliite leaves brown, Römerite leaves yellow; luster reads submetallic on Magnanelliite and vitreous on Römerite.
How to tell apart: Streak differs, so 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
Where rockhounds find magnanelliite
Classic worldwide localities
- La Fossa crater, Vulcano, Aeolian Islands, Italy
Field-hunting tip
Look in fumarolic sublimates country, 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
How do you identify magnanelliite?+
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What rocks look like magnanelliite?+
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Find magnanelliite on the map
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