Iyoite is a very rare member of the spinel supergroup, appearing as small black tabular crystals within manganese-rich metamorphic environments. It is scientifically significant due to its specific chemical composition and crystallography, making it primarily a target for advanced systematic mineral collectors.
Is this iyoite?
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 iyoite with a known reference. Iyoite sits at Mohs 5-6 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Iyoite leaves a black streak.
- 3Read the lusterHold the specimen under a strong light. Iyoite typically shows a metallic luster.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals.
Often confused with
Iyoite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Spinel is the harder of the two (Mohs 8 vs. 5-6); streak differs — Iyoite leaves black, Spinel leaves white; luster reads metallic on Iyoite and vitreous on Spinel.
How to tell apart: Streak differs — Iyoite leaves black, Hausmannite leaves brownish-red; luster reads metallic on Iyoite and submetallic on Hausmannite.
Often found alongside iyoite
Minerals reported to co-occur with iyoite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MnMgAl₂O₄
- Mohs hardness
- 5-6
- Density
- 4.9-5.1 g/cm³
- Colors
- Streak
- Black
- Luster
- Metallic
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Manganiferous Metamorphic Rocks
- Typical price
- n/a
Where rockhounds find iyoite
Classic worldwide localities
- Iyo Province, Japan
- Kagoshima Prefecture, Japan
Field-hunting tip
Look in manganiferous metamorphic rocks country — that is the host setting where iyoite typically forms. If you start seeing hausmannite, braunite, rhodochrosite in float, you are in the right ground. Field specimens usually show a tabular crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find iyoite on the map
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