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Kieftite is a rare cobalt antimonide mineral that forms part of the tilasite group, typically found in association with other cobalt minerals. It is identified primarily through laboratory analysis due to its visual similarity to more common metallic sulfides and arsenides.

Hardness
5-5.5
Mohs
Luster
Metallic
Streak
Gray
Transparency
Opaque

Is this kieftite?

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 kieftite with a known reference. Kieftite sits at Mohs 5-5.5, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: gray.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: metallic.
  • 4
    Match the color range
    Compare against the expected color range: tin white.
  • 5
    Look at form & habit
    Crystal system: cubic. Typical habit: anhedral grains and aggregates.

Often confused with

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

Skutterudite mineral
mineral
Skutterudite
Mohs 5.5-6

How to tell apart: Streak differs, so Kieftite leaves gray, Skutterudite leaves black.

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Cobaltite mineral
mineral
Cobaltite
Mohs 5.5

How to tell apart: Streak differs, so Kieftite leaves gray, Cobaltite leaves grayish black.

Compare →

Often found alongside kieftite

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

All properties

Chemical formula
CoSb₃
Mohs hardness
5-5.5
Density
7.2 g/cm³
Colors
Tin white
Streak
Gray
Luster
Metallic
Transparency
Opaque
Crystal system
Cubic
Crystal habit
Anhedral grains and aggregates
Cleavage
None
Rarity
Rare
Uses
Collector
Host rock
In a polymetallic sulfide skarn deposit

Where rockhounds find kieftite

Classic worldwide localities

  • Tunaberg, Sweden (type locality)

Field-hunting tip

Where it forms: In a polymetallic sulfide skarn deposit. If you start seeing chalcopyrite, dyscrasite, bornite in float, you are in the right ground. Typical habit: anhedral grains and aggregates. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify kieftite?+
Mohs hardness is 5-5.5. Luster: metallic. The streak is gray. Common colors include tin white.
Where is kieftite found?+
Notable localities include Tunaberg, Sweden (type locality).
Is kieftite safe to handle?+
Kieftite contains antimony and cobalt. Contains antimony and cobalt. Wash hands thoroughly after handling and avoid inhaling dust or powder during cutting or crushing.
What rocks look like kieftite?+
Kieftite is most often confused with Skutterudite, Cobaltite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with kieftite?+
Kieftite commonly co-occurs with Chalcopyrite, Dyscrasite, Bornite, Galena, Bismuth, Silver. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does kieftite form in?+
Where it forms: In a polymetallic sulfide skarn deposit. Working float back to the host body is the standard way to chase a fresh occurrence.
What is kieftite used for?+
Kieftite is used in collector.

Find kieftite on the map

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