Larisaite is a rare uranyl selenite mineral typically found as small yellow, tabular crystals or platy aggregates. It is highly sought after by collectors of radioactive mineral species due to its scarcity and distinct chemistry, and it is almost exclusively known from the Repete mine in Utah.
Is this larisaite?
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 larisaite with a known reference. Larisaite 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: yellow.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous; pearly on cleavage surfaces.
- 4Match the color rangeCompare against the expected color range: yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: lamellar.
Often confused with
Larisaite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Marthozite is the harder of the two (Mohs 6 vs. 1); streak differs, so Larisaite leaves yellow, Marthozite leaves pale yellow.
How to tell apart: Derriksite is the harder of the two (Mohs 2-3 vs. 1); streak differs, so Larisaite leaves yellow, Derriksite leaves pale green; luster reads vitreous; pearly on cleavage surfaces on Larisaite and adamantine on Derriksite.
Often found alongside larisaite
Minerals reported to co-occur with larisaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na(H₃O)(UO₂)₃(SeO₃)₂O₂·4H₂O
- Mohs hardness
- 1
- Density
- 4.46 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Vitreous; pearly on cleavage surfaces
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Lamellar
- Cleavage
- Perfect {010}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral in an oxidized ‘roll-front’ U deposit in sandstone
Where rockhounds find larisaite
Classic worldwide localities
- Repete mine, near Blanding, San Juan County, Utah, USA
Field-hunting tip
Where it forms: A secondary mineral in an oxidized ‘roll-front’ U deposit in sandstone. If you start seeing montmorillonite, quartz, haynesite in float, you are in the right ground. Typical habit: lamellar. Train your eye for that shape before scanning the outcrop.
Common questions
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Find larisaite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
