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, so 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, so 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, 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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