Rankamaite is a very rare tantalum-niobium oxide mineral typically found as fine, acicular, or fibrous aggregates in complex pegmatites. Due to its scarcity and small crystal size, it is a highly sought-after species for advanced mineral collectors specializing in rare earth or niobium-tantalum minerals. It is primarily identified by its occurrence in specific pegmatitic environments associated with other tantalum-bearing species.
Is this rankamaite?
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 rankamaite with a known reference. Rankamaite 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. Rankamaite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Rankamaite typically shows a adamantine luster.
- 4Match the color rangeCompare against the expected color range: yellow, colorless, white.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: acicular or fibrous crystals.
Often confused with
Rankamaite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Wodginite is the harder of the two (Mohs 5-6 vs. 3-4); streak differs — Rankamaite leaves white, Wodginite leaves yellowish brown; luster reads adamantine on Rankamaite and submetallic on Wodginite.
How to tell apart: Tantalite is the harder of the two (Mohs 6 vs. 3-4); streak differs — Rankamaite leaves white, Tantalite leaves black to reddish-brown; luster reads adamantine on Rankamaite and submetallic to resinous on Tantalite.
Often found alongside rankamaite
Minerals reported to co-occur with rankamaite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Na,K,Pb)₃(Ta,Nb,Al)₁₁O₃₀
- Mohs hardness
- 3-4
- Density
- 5.68 g/cm³
- Streak
- White
- Luster
- Adamantine
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Acicular or Fibrous Crystals
- Cleavage
- None
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Granite Pegmatites
- Typical price
- $200-1000+ per specimen
Where rockhounds find rankamaite
Classic worldwide localities
- Kivu province, Democratic Republic of the Congo
- Mano Kananga, DR Congo
Field-hunting tip
Look in granite pegmatites country — that is the host setting where rankamaite typically forms. If you start seeing tapiolite, microlite, tantalite in float, you are in the right ground. Field specimens usually show a acicular or fibrous crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find rankamaite on the map
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