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, so Iyoite leaves black, Spinel leaves white; luster reads metallic on Iyoite and vitreous on Spinel.
How to tell apart: Streak differs, so 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
Where rockhounds find iyoite
Classic worldwide localities
- Iyo Province, Japan
- Kagoshima Prefecture, Japan
Field-hunting tip
Look in manganiferous metamorphic rocks country, 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
How do you identify iyoite?+
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What rocks look like iyoite?+
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Find iyoite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
