Grantsite is an extremely rare hydrated sodium-uranium-vanadium mineral primarily found in the uranium-bearing sandstones of the Colorado Plateau. It usually appears as massive, earthy, yellow-colored crusts or coatings, making it difficult to distinguish visually from associated minerals like tyuyamunite without X-ray diffraction analysis.
Is this grantsite?
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 grantsite with a known reference. Grantsite sits at Mohs 1-2, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: olive-green to brownish green.
- 3Read the lusterHold the specimen under a strong light. Luster: silky or pearly to subadamantine.
- 4Match the color rangeCompare against the expected color range: green black, dark green, olive green.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: bladed, crystalline, fibrous.
Often confused with
Grantsite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Grantsite leaves olive-green to brownish green, Carnotite leaves strontian-yellow; luster reads silky or pearly to subadamantine on Grantsite and dull, earthy; silky when crystalline on Carnotite.
How to tell apart: Streak differs, so Grantsite leaves olive-green to brownish green, Tyuyamunite leaves light yellow; luster reads silky or pearly to subadamantine on Grantsite and adamantine, pearly on {001}, may be dull to waxy if massive on Tyuyamunite.
Often found alongside grantsite
Minerals reported to co-occur with grantsite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,Ca)₂+x(V,V)₆O₁₆·4H₂O
- Mohs hardness
- 1-2
- Density
- 2.94 g/cm³
- Colors
- Streak
- Olive-green to brownish green
- Luster
- Silky or pearly to subadamantine
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Bladed, crystalline, fibrous
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In partially oxidized portions of sandstone seams and coalified wood in vanadiferous uranium deposits of the Colorado Plateau type
Where rockhounds find grantsite
Classic worldwide localities
- F-33 mine (T12N-R9W Sec 33) 10 km NE of Grants, Valencia County, New Mexico (type locality)
Field-hunting tip
Where it forms: In partially oxidized portions of sandstone seams and coalified wood in vanadiferous uranium deposits of the Colorado Plateau type. If you start seeing haggite, paramontroseite, corvusite in float, you are in the right ground. Typical habit: bladed, crystalline, fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify grantsite?+
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Find grantsite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
