Osakaite is a rare zinc sulfate mineral that typically forms as delicate, transparent platy crystals within oxidized zones of zinc deposits. It is a secondary mineral commonly found encrusting other zinc species, requiring microscopic inspection for positive identification. It was first described from material found in the Osaka Prefecture, Japan.
Is this osakaite?
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 osakaite with a known reference. Osakaite sits at Mohs 1, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white to pale blue.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly.
- 4Match the color rangeCompare against the expected color range: white, pale blue.
- 5Look at form & habitCrystal system: triclinic. Typical habit: hexagonal, platy, stalactitic.
Often confused with
Osakaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Hydrozincite is the harder of the two (Mohs 2-2.5 vs. 1).
How to tell apart: Gunningite is the harder of the two (Mohs ~2.5 vs. 1); luster reads pearly on Osakaite and vitreous on Gunningite.
How to tell apart: Goslarite is the harder of the two (Mohs 2-2.5 vs. 1); luster reads pearly on Osakaite and vitreous, silky if fibrous on Goslarite.
Often found alongside osakaite
Minerals reported to co-occur with osakaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Zn₄SO₄(OH)₆·5H₂O
- Mohs hardness
- 1
- Density
- 2.7 g/cm³
- Streak
- White to pale blue
- Luster
- Pearly
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Hexagonal, platy, stalactitic
- Cleavage
- Perfect, {001}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral on mine walls and fractures produced by reaction of oxygenated groundwater with a polymetallic sulfide deposit
Where rockhounds find osakaite
Classic worldwide localities
- Hirao Mine, Osaka Prefecture, Japan
Field-hunting tip
Where it forms: A secondary mineral on mine walls and fractures produced by reaction of oxygenated groundwater with a polymetallic sulfide deposit. If you start seeing hydrozincite, smithsonite, chlorite in float, you are in the right ground. Typical habit: hexagonal, platy, stalactitic. Train your eye for that shape before scanning the outcrop.
Common questions
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Find osakaite on the map
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