Vanarsite is a rare sodium calcium arsenic oxide, typically very dark blue. It is a secondary mineral formed by the oxidation of montroseite-corvusite assemblages in a moist environment. It was first described from Packrat mine, Gateway district, Mesa County, Colorado, USA.
Is this vanarsite?
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 vanarsite with a known reference. Vanarsite sits at Mohs ~2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: grayish blue.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: very dark blue.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: crusts, aggregates of lath-like crystals.
Often confused with
Vanarsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Vanarsite leaves grayish blue, Pascoite leaves cadmium-yellow.
How to tell apart: Vanarsite is noticeably harder (Mohs ~2 vs. ~1); streak differs, so Vanarsite leaves grayish blue, Hewettite leaves brownish red; luster reads vitreous on Vanarsite and silky to adamantine on Hewettite.
Often found alongside vanarsite
Minerals reported to co-occur with vanarsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCa₁₂(As³⁺V⁵⁺₈.₅V⁴⁺₃.₅As⁵⁺₆O₅₁)₂·78H₂O
- Mohs hardness
- ~2
- Density
- 2.48 g/cm³
- Colors
- Very dark blue
- Streak
- Grayish blue
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Crusts, aggregates of lath-like crystals
- Cleavage
- Fair on {100}
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A secondary mineral formed by the oxidation of montroseite-corvusite assemblages in a moist environment
Where rockhounds find vanarsite
Classic worldwide localities
- Packrat mine, Gateway district, Mesa County, Colorado, USA
Field-hunting tip
Where it forms: A secondary mineral formed by the oxidation of montroseite-corvusite assemblages in a moist environment. If you start seeing gatewayite, morrisonite, packratite in float, you are in the right ground. Typical habit: crusts, aggregates of lath-like crystals. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify vanarsite?+
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Find vanarsite on the map
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