Ianthinite is a rare, highly sensitive uranium-bearing mineral recognizable by its distinct deep violet color. It is an alteration product of uraninite and is often found as a surface coating or in fragile crystal groups, commonly turning into yellow schoepite upon exposure to air.
Is this ianthinite?
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 ianthinite with a known reference. Ianthinite sits at Mohs 2-3, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dull violet-brown.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to submetallic.
- 4Match the color rangeCompare against the expected color range: violet black, violet, violet purple.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular, granular.
Often confused with
Ianthinite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Ianthinite leaves dull violet-brown, Becquerelite leaves yellow; luster reads vitreous to submetallic on Ianthinite and adamantine to greasy on Becquerelite.
How to tell apart: Streak differs, so Ianthinite leaves dull violet-brown, Masuyite leaves orange-yellow.
How to tell apart: Streak differs, so Ianthinite leaves dull violet-brown, Schoepite leaves yellow; luster reads vitreous to submetallic on Ianthinite and adamantine on Schoepite.
Often found alongside ianthinite
Minerals reported to co-occur with ianthinite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- U₂(UO₂)₄O₆(OH)₄·9H₂O
- Mohs hardness
- 2-3
- Density
- 5.16 g/cm³
- Colors
- Streak
- Dull violet-brown
- Luster
- Vitreous to submetallic
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular, granular
- Cleavage
- {001}, perfect; {100}, good
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare secondary mineral in the unoxidized portions of uranium deposits
Where rockhounds find ianthinite
Classic worldwide localities
- Marshall Pass district, Gunnison and Saguache Co., Colorado, and in the Lucky Strike mine, La Sal Mountains, San Juan Co., Utah, USA
- Shinkolobwe, Katanga Province, Congo (Shaba Province, Zaire)
- Wölsendorf, Bavaria, and Menzenschwand, Black Forest, Germany
- Sabugal, Portugal
- La Crouzille, Haute-Vienne, France
- Bigay, and Les Bois Noirs, Puy-de-Dôme, France
Field-hunting tip
Where it forms: A rare secondary mineral in the unoxidized portions of uranium deposits. If you start seeing uraninite, schoepite, becquerelite in float, you are in the right ground. Typical habit: acicular, granular. Train your eye for that shape before scanning the outcrop.
Common questions
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Find ianthinite on the map
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