Simpsonite is a rare aluminum tantalum oxide mineral typically found in highly evolved granite pegmatites. Collectors look for its characteristic yellowish, prismatic crystals which often display a distinct bright yellow fluorescence under shortwave ultraviolet light.
Is this simpsonite?
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 simpsonite with a known reference. Simpsonite sits at Mohs 7.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: adamantine.
- 4Match the color rangeCompare against the expected color range: brownish yellow, colorless, white, light brown, light yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: euhedral crystals, prismatic, striated.
Often confused with
Simpsonite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside simpsonite
Minerals reported to co-occur with simpsonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Al₄Ta₃O₁₃(OH)
- Mohs hardness
- 7.5
- Density
- 6.68-6.82 g/cm³
- Streak
- White
- Luster
- Adamantine
- Transparency
- Semitransparent
- Crystal system
- Trigonal
- Crystal habit
- Euhedral crystals, prismatic, striated
- Cleavage
- None
- Fluorescence
- Blue white under SW and LW UV
- Rarity
- Rare
- Uses
- Collector, Ore of tantalum
- Host rock
- An uncommon accessory mineral in some tantalum-rich granite pegmatites
Where rockhounds find simpsonite
Classic worldwide localities
- Tabba Tabba, Western Australia
- Alto do Giz pegmatite, near Parelhas, and the Onça mine, about 25 km distant, Rio Grande do Norte, Brazil
- Al Hayat and Mdara mines, Bikita, and at the Benson No. 3 pegmatite, Mtoko, Zimbabwe
- Congo (Zaire), from Mumba, near Lake Kivu, Kivu Province, and in the Manono pegmatite, Katanga (Shaba) Province
- Leshaia pegmatite, Vuoriyarvi carbonatite complex, Kola Peninsula, Russia
- Tanco pegmatite, Bernic Lake, Manitoba, Canada
Field-hunting tip
Where it forms: An uncommon accessory mineral in some tantalum-rich granite pegmatites. If you start seeing tantalite, manganotantalite, microlite in float, you are in the right ground. Typical habit: euhedral crystals, prismatic, striated. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify simpsonite?+
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What rocks look like simpsonite?+
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Find simpsonite on the map
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