Fersmite is a rare niobium-rich mineral that typically forms as small, elongated prismatic crystals in carbonatites and alkaline pegmatites. Collectors often identify it by its dark color, sub-metallic luster, and its characteristic occurrence alongside calcite and other rare-earth minerals.
Is this fersmite?
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 fersmite with a known reference. Fersmite sits at Mohs 4-4.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: grayish brown.
- 3Read the lusterHold the specimen under a strong light. Luster: resinous to subvitreous, submetallic.
- 4Match the color rangeCompare against the expected color range: black, brownish black, dark brown.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: metamict, prismatic.
Often confused with
Fersmite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Columbite is the harder of the two (Mohs 6 vs. 4-4.5); streak differs, so Fersmite leaves grayish brown, Columbite leaves blackish brown; luster reads resinous to subvitreous, submetallic on Fersmite and submetallic on Columbite.
How to tell apart: Euxenite-(Y) is the harder of the two (Mohs 5.5-6.5 vs. 4-4.5); streak differs, so Fersmite leaves grayish brown, Euxenite-(Y) leaves yellowish, grayish, or reddish brown; luster reads resinous to subvitreous, submetallic on Fersmite and brilliant submetallic, waxy to resinous on fractures on Euxenite-(Y).
Often found alongside fersmite
Minerals reported to co-occur with fersmite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaNb₂O₆
- Mohs hardness
- 4-4.5
- Density
- 4.69-4.80 g/cm³
- Streak
- Grayish brown
- Luster
- Resinous to subvitreous, submetallic
- Transparency
- Opaque, translucent through thin edges
- Crystal system
- Orthorhombic
- Crystal habit
- Metamict, prismatic
- Cleavage
- {100}, parting
- Rarity
- Rare
- Uses
- Collector
- Host rock
- A rare accessory mineral in nepheline syenites and carbonatites
Where rockhounds find fersmite
Classic worldwide localities
- Dark Star claim, 8 km south of Alta, Ravalli Co., Montana, USA
- Gem Park ultramafic complex, about six km east of Hillside, Fremont Co., Colorado, USA
- Mesa Grande and Ramona districts, San Diego Co., California, USA
- Foote mine, Kings Mountain, Cleveland Co., North Carolina, USA
- Lake Buldym, Vishnevy-Ilmen Mountains, Southern Ural Mountains, Russia
- Alpe Rosso, near Orcesco, Val Vigezzo, Piedmont, Italy
Field-hunting tip
Where it forms: A rare accessory mineral in nepheline syenites and carbonatites. If you start seeing columbite, pyrochlore, plagioclase in float, you are in the right ground. Typical habit: metamict, prismatic. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify fersmite?+
Where is fersmite found?+
Is fersmite safe to handle?+
What rocks look like fersmite?+
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Find fersmite on the map
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