Bannermanite is an exceptionally rare vanadium oxide mineral found in volcanic fumaroles. It typically occurs as small, black, acicular crystal aggregates and is primarily valued by advanced mineral collectors for its unique geological origin.
Is this bannermanite?
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 bannermanite with a known reference. Bannermanite sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: dark gray-black.
- 3Read the lusterHold the specimen under a strong light. Luster: submetallic.
- 4Match the color rangeCompare against the expected color range: black.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: lath, microscopic crystals.
Often confused with
Bannermanite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Bannermanite leaves dark gray-black, Vanadinite leaves white to pale red or pale yellow; luster reads submetallic on Bannermanite and subresinous to subadamantine on Vanadinite.
How to tell apart: Streak differs, so Bannermanite leaves dark gray-black, Descloizite leaves orange to brownish red; luster reads submetallic on Bannermanite and greasy on Descloizite.
Often found alongside bannermanite
Minerals reported to co-occur with bannermanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,K)xVxV₆-xO₁₅ (0.5<x<0.9)
- Mohs hardness
- 3-4
- Density
- 3.5 g/cm³
- Colors
- Streak
- Dark gray-black
- Luster
- Submetallic
- Transparency
- Opaque, transparent on thin edges
- Crystal system
- Monoclinic
- Crystal habit
- Lath, microscopic crystals
- Cleavage
- {100}, perfect; {010}, fair
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In vanadium-bearing sublimates in fumaroles on a basaltic volcanic cone
Where rockhounds find bannermanite
Classic worldwide localities
- Izalco volcano, El Salvador
Field-hunting tip
Where it forms: In vanadium-bearing sublimates in fumaroles on a basaltic volcanic cone. If you start seeing shcherbinaite, stoiberite, ziesite in float, you are in the right ground. Typical habit: lath, microscopic crystals. Train your eye for that shape before scanning the outcrop.
Common questions
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Find bannermanite on the map
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