Haiweeite is a rare calcium uranyl silicate that typically forms as delicate, radiating, fan-shaped clusters or soft, powdery coatings. It is highly sought after by collectors for its brilliant neon-green fluorescence under short-wave ultraviolet light, although it requires cautious handling due to its radioactive nature.
Is this haiweeite?
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 haiweeite with a known reference. Haiweeite sits at Mohs 3.5, 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: pearly on the cleavage.
- 4Match the color rangeCompare against the expected color range: greenish yellow, light yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: aggregates, microscopic crystals, spherical.
Often confused with
Haiweeite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Haiweeite is noticeably harder (Mohs 3.5 vs. 2.5); streak differs, so Haiweeite leaves white, Uranophane leaves yellowish white; luster reads pearly on the cleavage on Haiweeite and vitreous on Uranophane.
How to tell apart: Haiweeite is noticeably harder (Mohs 3.5 vs. 2-2.5); streak differs, so Haiweeite leaves white, Autunite leaves pale yellow; luster reads pearly on the cleavage on Haiweeite and vitreous, pearly on {001} on Autunite.
Often found alongside haiweeite
Minerals reported to co-occur with haiweeite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca(UO₂)₂Si₅O₁₂(OH)₂·6H₂O
- Mohs hardness
- 3.5
- Density
- 3.35 g/cm³
- Streak
- White
- Luster
- Pearly on the cleavage
- Transparency
- Semitransparent
- Crystal system
- Orthorhombic
- Crystal habit
- Aggregates, microscopic crystals, spherical
- Cleavage
- Good on {100}
- Fluorescence
- Weak dull green under SW and LW UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- On fracture surfaces in granite and in voids in neighboring loosely consolidated lake bed sediments (Coso Mountains, California, USA); along fractures in tourmaline-bearing granite and granite pegmatite (Brazil)
Where rockhounds find haiweeite
Classic worldwide localities
- Haiwee Reservoir, Coso Mountains, Inyo Co., California, USA
- Perus, 25 km north of São Paulo, and from Teofilo Otoni, Minas Gerais, Brazil
- Portezuelo Hill, Ranquil district, Mendoza Province, Argentina
- Badgastein, Salzburg, Austria
Field-hunting tip
Where it forms: On fracture surfaces in granite and in voids in neighboring loosely consolidated lake bed sediments (Coso Mountains, California, USA); along fractures in tourmaline-bearing granite and granite pegmatite (Brazil). If you start seeing autunite, meta-autunite, uranophane in float, you are in the right ground. Typical habit: aggregates, microscopic crystals, spherical. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify haiweeite?+
Where is haiweeite found?+
Is haiweeite safe to handle?+
What rocks look like haiweeite?+
What minerals are found with haiweeite?+
What kind of rock does haiweeite form in?+
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Find haiweeite on the map
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