Gunterite is an extremely rare hydrous sodium vanadate that typically occurs as thin, yellow, platy crystals or efflorescent crusts. It is most commonly found as a secondary mineral in vanadium-rich uranium deposits within sandstone, often appearing in association with other rare vanadates.
Is this gunterite?
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 gunterite with a known reference. Gunterite 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: subadamantine.
- 4Match the color rangeCompare against the expected color range: orange-yellow.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: platy crystals, crusts.
Often confused with
Gunterite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Sherwoodite is the harder of the two (Mohs ~2 vs. ~1); streak differs, so Gunterite leaves yellow, Sherwoodite leaves pale blue; luster reads subadamantine on Gunterite and vitreous to earthy on Sherwoodite.
How to tell apart: Pascoite is the harder of the two (Mohs ~2.5 vs. ~1); streak differs, so Gunterite leaves yellow, Pascoite leaves cadmium-yellow; luster reads subadamantine on Gunterite and vitreous to subadamantine on Pascoite.
Often found alongside gunterite
Minerals reported to co-occur with gunterite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Na₄Ca[V₁₀O₂₈]·20H₂O
- Mohs hardness
- ~1
- Density
- 2.398 g/cm³
- Colors
- Streak
- Yellow
- Luster
- Subadamantine
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
- Crystal habit
- Platy crystals, crusts
- Cleavage
- {001}, {100}, {010}; imperfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In efflorescencent crusts on mine walls and in fractures in sandstone, formed by the oxidation of montroseite–corvusite assemblages
Where rockhounds find gunterite
Classic worldwide localities
- West Sunday mine, Slick Rock district, San Miguel County, Colorado, USA
Field-hunting tip
Where it forms: In efflorescencent crusts on mine walls and in fractures in sandstone, formed by the oxidation of montroseite–corvusite assemblages. If you start seeing montroseite, corvusite, huemulite in float, you are in the right ground. Typical habit: platy crystals, crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify gunterite?+
Where is gunterite found?+
Is gunterite safe to handle?+
What rocks look like gunterite?+
What minerals are found with gunterite?+
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Find gunterite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
