Kotoite is a rare borate mineral that typically forms in contact-metamorphosed limestone or dolomite deposits. It is most easily identified by its occurrence in specific skarn assemblages alongside minerals like ludwigite and suanite, appearing as white or colorless granular masses.
Is this kotoite?
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 kotoite with a known reference. Kotoite sits at Mohs 6.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Kotoite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Kotoite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, gray, yellow, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: granular, massive, or coarse crystalline aggregates.
Often confused with
Kotoite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside kotoite
Minerals reported to co-occur with kotoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Mg₃(BO₃)₂
- Mohs hardness
- 6.5
- Density
- 3.12 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Granular, Massive, Or Coarse Crystalline Aggregates
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector, Scientific Research
- Host rock
- Metamorphosed Dolomite Marble in Contact Zones
- Typical price
- $20-100 per specimen
Where rockhounds find kotoite
Classic worldwide localities
- Hol Kol Mine, Suan, North Korea
- Kearsarge, California, USA
- Brooks Mountain, Alaska, USA
- Dashkesan, Azerbaijan
Field-hunting tip
Look in metamorphosed dolomite marble in contact zones country — that is the host setting where kotoite typically forms. If you start seeing ludwigite, suanite, forsterite in float, you are in the right ground. Field specimens usually show a granular, massive, or coarse crystalline aggregates habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find kotoite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
