Bunnoite is a rare manganese aluminum silicate that forms dull green foliated to granular crystals. It occurs in veinlets cutting metamorphosed iron- and manganese-rich marine sediments. Associated minerals include stilpnomelane, rhodonite and piemontite. It was first described from Kamo Mountain, Ino, Kochi Prefecture, Japan.
Is this bunnoite?
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 bunnoite with a known reference. Bunnoite sits at Mohs 5.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Bunnoite leaves a dull green streak.
- 3Read the lusterHold the specimen under a strong light. Bunnoite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: dull green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: foliated to granular crystals.
Often confused with
Bunnoite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Bunnoite is noticeably harder (Mohs 5.5 vs. 2); streak differs, so Bunnoite leaves dull green, Retgersite leaves pale green.
How to tell apart: Bunnoite is noticeably harder (Mohs 5.5 vs. 2-2.5); streak differs, so Bunnoite leaves dull green, Morenosite leaves white.
Often found alongside bunnoite
Minerals reported to co-occur with bunnoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mn²⁺₆AlSi₆O₁₈(OH)₃
- Mohs hardness
- 5.5
- Density
- 3.63 g/cm³
- Colors
- Streak
- Dull Green
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Foliated to Granular Crystals
- Cleavage
- Perfect On {012}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Oxidized Zones of Nickel-rich Sulfide Deposits
Where rockhounds find bunnoite
Classic worldwide localities
- Bunno, Japan
- various mine dumps worldwide
Field-hunting tip
Look in oxidized zones of nickel-rich sulfide deposits country, the host setting where bunnoite typically forms. If you start seeing morenosite, retgersite, nickel-bearing sulfides in float, you are in the right ground. Field specimens usually show a foliated to granular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find bunnoite on the map
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