Bassetite is a rare hydrated iron uranyl phosphate that typically occurs as thin, yellow-green tabular crystals. It is frequently found in the oxidation zones of uranium-bearing hydrothermal veins and is highly prized by collectors for its brilliant fluorescence.
Is this bassetite?
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 bassetite with a known reference. Bassetite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: greenish white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, bronzy on {010}.
- 4Match the color rangeCompare against the expected color range: yellow, bronze, brownish yellow, greenish brown, olive green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: tabular crystals, micaceous aggregates, crusts.
Often confused with
Bassetite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Bassetite leaves greenish white, Autunite leaves pale yellow.
How to tell apart: Streak differs, so Bassetite leaves greenish white, Meta-autunite leaves yellow; luster reads vitreous, bronzy on {010} on Bassetite and pearly to dull on Meta-autunite.
How to tell apart: Streak differs, so Bassetite leaves greenish white, Torbernite leaves pale green.
Often found alongside bassetite
Minerals reported to co-occur with bassetite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe(UO₂)₂(PO₄)₂(H₂O)₁₀
- Mohs hardness
- 2.5
- Density
- 3.40-3.63 g/cm³
- Streak
- Greenish white
- Luster
- Vitreous, bronzy on {010}
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Tabular crystals, micaceous aggregates, crusts
- Cleavage
- {010}, perfect; {100} and {001}, distinct
- Fluorescence
- Bright yellowish-green under UV
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in the oxidized zone of some uranium-bearing hydrothermal mineral deposits
Where rockhounds find bassetite
Classic worldwide localities
- Overland Mountain, Jamestown district, Boulder Co., Colorado, USA
- Denise No. 1 mine and in the Fuemrol mine, Temple Mountain, Emery Co., Utah, USA
- Sue and Red Bluff mines, Sierra Ancha Mountains, and widespread in the Dripping Springs quartzite in the northwestern part of Gila Co., Arizona, USA
- Merry Widow mine, Grant Co., New Mexico, USA
- Basset group of mines, Illogan, and the South Terras mine, St. Stephen-in-Brannel, Cornwall, England
- Arcu su Linnarbu, Capoterra, near Cagliari, Sardinia, Italy
Field-hunting tip
Where it forms: A rare secondary mineral in the oxidized zone of some uranium-bearing hydrothermal mineral deposits. If you start seeing uranospathite, torbernite, uraninite in float, you are in the right ground. Typical habit: tabular crystals, micaceous aggregates, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
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Find bassetite on the map
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