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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: white, colorless.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: massive.
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
- 3.10 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Massive
- Cleavage
- On {110}, perfect; a parting on {101}
- Rarity
- Rare
- Uses
- Collector, Scientific research
- Host rock
- An uncommon mineral typically formed in the contact zone of magnesium-rich skarn borate deposits
Where rockhounds find kotoite
Classic worldwide localities
- Jumbo Mountain, south of Darrington, Snohomish Co., Washington, and near Brighton, Big Cottonwood district, Salt Lake Co., Utah, USA
- Hol Kol Au–Cu mine, about 75 km southeast of Pyongyang, Suan Co., North Korea
- Neichi mine, Miyako, Iwate Prefecture, Japan
- Qiliping, Hunan Province, and near Dading, Guizhou Province, China
- Korotkov skarn deposit, central Transbaikal, and at the Titovskoye boron deposit, Tas-Khayakhtakh Mountains, Sakha, Russia
- Băiţa (Rézbánya), Romania
Field-hunting tip
Where it forms: An uncommon mineral typically formed in the contact zone of magnesium-rich skarn borate deposits. If you start seeing forsterite, clinohumite, ludwigite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify kotoite?+
Where is kotoite found?+
What rocks look like kotoite?+
What minerals are found with kotoite?+
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Find kotoite on the map
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