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Kimrobinsonite is a very rare tantalum hydroxide mineral typically found as small, cubic crystals within highly evolved granitic pegmatites. It is primarily identified through chemical analysis due to its scarcity and similarity to other members of the pyrochlore supergroup.

Hardness
2.5
Mohs
Luster
Dull chalky
Streak
White
Transparency
Semitransparent

Is this kimrobinsonite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

  • 1
    Test the hardness
    Try to scratch kimrobinsonite with a known reference. Kimrobinsonite sits at Mohs 2.5, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: white.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: dull chalky.
  • 4
    Match the color range
    Compare against the expected color range: lemon white.
  • 5
    Look at form & habit
    Crystal system: cubic. Typical habit: cryptocrystalline, earthy, friable.

Often confused with

Kimrobinsonite vs. its common look-alikes, and how to tell them apart in the field.

Dark brown pyrochlore octahedron
mineral
Pyrochlore
Mohs 5-5.5

How to tell apart: Pyrochlore is the harder of the two (Mohs 5-5.5 vs. 2.5); streak differs, so Kimrobinsonite leaves white, Pyrochlore leaves brown; luster reads dull chalky on Kimrobinsonite and vitreous to resinous on Pyrochlore.

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Often found alongside kimrobinsonite

Minerals reported to co-occur with kimrobinsonite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula
Ta(OH)₃(O,CO₃)
Mohs hardness
2.5
Density
6.865 g/cm³
Colors
Lemon white
Streak
White
Luster
Dull chalky
Transparency
Semitransparent
Crystal system
Cubic
Crystal habit
Cryptocrystalline, earthy, friable
Cleavage
None
Rarity
Rare
Uses
Collector
Host rock
The weathering product of an undetermined Ta–Sb pegmatite mineral

Where rockhounds find kimrobinsonite

Classic worldwide localities

  • Mt. Holland, Western Australia (type locality)

Field-hunting tip

Where it forms: The weathering product of an undetermined Ta–Sb pegmatite mineral. If you start seeing cesstibtantite, manganotantalite, antimonian microlite in float, you are in the right ground. Typical habit: cryptocrystalline, earthy, friable. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kimrobinsonite?+
Mohs hardness is 2.5. Luster: dull chalky. The streak is white. Common colors include lemon white.
Where is kimrobinsonite found?+
Notable localities include Mt. Holland, Western Australia (type locality).
What rocks look like kimrobinsonite?+
Kimrobinsonite is most often confused with Pyrochlore. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with kimrobinsonite?+
Kimrobinsonite commonly co-occurs with Cesstibtantite, Manganotantalite, Antimonian microlite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does kimrobinsonite form in?+
Where it forms: The weathering product of an undetermined Ta–Sb pegmatite mineral. Working float back to the host body is the standard way to chase a fresh occurrence.
What is kimrobinsonite used for?+
Kimrobinsonite is used in collector.

Find kimrobinsonite on the map

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