Castellaroite is a rare manganese arsenate mineral found as small, vibrant yellow tabular crystals. It is primarily known from the Molinello mine in Italy, where it occurs in manganese-rich mineral assemblages.
Is this castellaroite?
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 castellaroite with a known reference. Castellaroite 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to silky.
- 4Match the color rangeCompare against the expected color range: colorless.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals.
Often confused with
Castellaroite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Brandtite is the harder of the two (Mohs 3.5 vs. 2.5).
How to tell apart: Tilasite is the harder of the two (Mohs 5 vs. 2.5); luster reads vitreous to silky on Castellaroite and resinous, vitreous on cleavages on Tilasite.
Often found alongside castellaroite
Minerals reported to co-occur with castellaroite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₃(AsO₄)₂·4.5H₂O
- Mohs hardness
- 2.5
- Density
- 3.14 g/cm³
- Colors
- Streak
- White
- Luster
- Vitreous to silky
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals
- Cleavage
- Perfect on {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral precipitated from oxidizing hydrothermal fluids
Where rockhounds find castellaroite
Classic worldwide localities
- Monte Nero mine, Rocchetta Vara, La Spezia, Liguria, and the Valletta mine, near Canosio, Cuneo, Piedmont, Italy
Field-hunting tip
Where it forms: A secondary mineral precipitated from oxidizing hydrothermal fluids. If you start seeing coralloite, manganohörnesite, rhodochrosite in float, you are in the right ground. Typical habit: tabular crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify castellaroite?+
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Is castellaroite safe to handle?+
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Find castellaroite on the map
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