Tiragalloite is a rare manganese arsenic silicate primarily known from the Gambatesa mine in Italy. It typically occurs as small orange tabular crystals and is highly prized by collectors of rare mineral species due to its restricted locality and complex chemistry.
Is this tiragalloite?
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 tiragalloite with a known reference. Tiragalloite sits at Mohs 4-5, 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: subadamantine.
- 4Match the color rangeCompare against the expected color range: orange.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, prismatic.
Often confused with
Tiragalloite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside tiragalloite
Minerals reported to co-occur with tiragalloite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn₄AsSi₃O₁₂(OH)
- Mohs hardness
- 4-5
- Density
- 3.84 g/cm³
- Colors
- Streak
- White
- Luster
- Subadamantine
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, prismatic
- Cleavage
- Good on {100}; a distinct parting, normal to elongation
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In veinlets cutting massive aggregates of braunite and quartz (Molinello mine, Italy); in manganese-rich lenses in quartzitic chlorite schists probably derived from marine sediments (Ködnitz Valley, Austria)
Where rockhounds find tiragalloite
Classic worldwide localities
- Molinello manganese mine, Val Graveglia, near Chiavari, Liguria, Italy
- Ködnitz Valley, Tirol, Austria
Field-hunting tip
Where it forms: In veinlets cutting massive aggregates of braunite and quartz (Molinello mine, Italy); in manganese-rich lenses in quartzitic chlorite schists probably derived from marine sediments (Ködnitz Valley, Austria). If you start seeing quartz, manganoan calcite, parsettensite in float, you are in the right ground. Typical habit: acicular, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find tiragalloite on the map
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