Gatewayite is a calcium arsenic vanadium oxide, typically very dark greenish 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 gatewayite?
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 gatewayite with a known reference. Gatewayite 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 greenish blue.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: massive.
Often confused with
Gatewayite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Chert is the harder of the two (Mohs 6.5-7 vs. ~2); streak differs, so Gatewayite leaves grayish blue, Chert leaves white; luster reads vitreous on Gatewayite and waxy on Chert.
How to tell apart: Chalcedony is the harder of the two (Mohs 6.5-7 vs. ~2); streak differs, so Gatewayite leaves grayish blue, Chalcedony leaves white; luster reads vitreous on Gatewayite and waxy on Chalcedony.
How to tell apart: Jasper is the harder of the two (Mohs 6.5-7 vs. ~2); streak differs, so Gatewayite leaves grayish blue, Jasper leaves white; luster reads vitreous on Gatewayite and waxy on Jasper.
Often found alongside gatewayite
Minerals reported to co-occur with gatewayite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₆(As³⁺V⁴⁺₃V⁵⁺₉As⁵⁺₆O₅₁)·31H₂O
- Mohs hardness
- ~2
- Density
- 2.34 g/cm³
- Colors
- Very dark greenish blue
- Streak
- Grayish blue
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Massive
- Cleavage
- Fair on {010} and {101}
- Rarity
- Common
- Uses
- Lapidary, Collector
- Host rock
- A secondary mineral formed by the oxidation of montroseite-corvusite assemblages in a moist environment
Where rockhounds find gatewayite
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 morrisonite, packratite, vanarsite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.
Common questions
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Find gatewayite on the map
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