Tuhualite is an extremely rare cyclosilicate mineral typically found in volcanic rocks. It is most famous for its distinctive deep violet-blue color and tabular habit, primarily occurring in specific peralkaline rhyolite deposits.
Is this tuhualite?
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 tuhualite with a known reference. Tuhualite sits at Mohs 4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Tuhualite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Tuhualite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: deep blue, violet-blue, purple.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: tabular crystals, massive.
Often confused with
Tuhualite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Osumilite is the harder of the two (Mohs 5-5.5 vs. 4).
How to tell apart: Milarite is the harder of the two (Mohs 5.5-6 vs. 4).
How to tell apart: Cordierite is the harder of the two (Mohs 7-7.5 vs. 4).
Often found alongside tuhualite
Minerals reported to co-occur with tuhualite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,K)Fe²⁺₂Fe³⁺₂Si₁₂O₃₀
- Mohs hardness
- 4
- Density
- 2.92 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Tabular Crystals, Massive
- Cleavage
- Poor
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Peralkaline Rhyolitic Volcanic Rocks
- Typical price
- $100-500 per specimen
Where rockhounds find tuhualite
Classic worldwide localities
- Mayor Island, New Zealand
- Eifel region, Germany
Field-hunting tip
Look in peralkaline rhyolitic volcanic rocks country, the host setting where tuhualite typically forms. If you start seeing aegirine, arfvedsonite, quartz in float, you are in the right ground. Field specimens usually show a tabular crystals, massive habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find tuhualite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
