Vonsenite is a rare iron-rich borate mineral typically found as black, acicular, or prismatic crystals within contact metamorphic zones. It is often distinguished from similar iron minerals by its occurrence in specific boron-bearing skarns and its submetallic luster.
Is this vonsenite?
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 vonsenite with a known reference. Vonsenite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: brownish black.
- 3Read the lusterHold the specimen under a strong light. Luster: metallic to submetallic, silky if fibrous.
- 4Match the color rangeCompare against the expected color range: black, greenish black.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: fibrous, prismatic, radial.
Often confused with
Vonsenite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Vonsenite leaves brownish black, Ludwigite leaves black to greenish black; luster reads metallic to submetallic, silky if fibrous on Vonsenite and submetallic on Ludwigite.
How to tell apart: Streak differs, so Vonsenite leaves brownish black, Ilvaite leaves black, inclining to green or brown; luster reads metallic to submetallic, silky if fibrous on Vonsenite and submetallic on Ilvaite.
How to tell apart: Streak differs, so Vonsenite leaves brownish black, Magnetite leaves black.
Often found alongside vonsenite
Minerals reported to co-occur with vonsenite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Fe₂²⁺Fe³⁺BO₅
- Mohs hardness
- 5
- Density
- 4.21 g/cm³
- Colors
- Streak
- Brownish black
- Luster
- Metallic to submetallic, silky if fibrous
- Transparency
- Opaque
- Crystal system
- Orthorhombic
- Crystal habit
- Fibrous, prismatic, radial
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector, Research
- Host rock
- Uncommon in boron-rich skarns
Where rockhounds find vonsenite
Classic worldwide localities
- Old City quarry, Riverside, Riverside Co., California, USA
- Jayville magnetite mine, Stevens Co., New York, USA
- Northwest flank of Brooks Mountain, Seward Peninsula, Alaska, USA
- Kamaishi mine, Iwate Prefecture, and at the Sengendera mine, Miyazaki Prefecture, Japan
- Dading tin-iron deposits, Guizhou Province, China
- Cura di Vetralla, and at Montalto di Castro, Lazio, Italy
Field-hunting tip
Where it forms: Uncommon in boron-rich skarns. If you start seeing magnetite, pyroxene, pyrrhotite in float, you are in the right ground. Typical habit: fibrous, prismatic, radial. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify vonsenite?+
Where is vonsenite found?+
What rocks look like vonsenite?+
What minerals are found with vonsenite?+
What kind of rock does vonsenite form in?+
What is vonsenite used for?+
Find vonsenite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
