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Cafarsite is a rare calcium-titanium-iron arsenite mineral known almost exclusively from the Binn Valley of Switzerland. It typically appears as dark, complex dodecahedral crystals embedded in dolomite marble and is highly prized by advanced mineral collectors for its unique chemistry and crystallography.

Hardness
5.5-6
Mohs
Luster
Submetallic
Streak
Yellow-brown
Transparency
Opaque to translucent in thin fragments

Is this cafarsite?

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 cafarsite with a known reference. Cafarsite sits at Mohs 5.5-6, softer than the next harder reference, harder than the previous one.
  • 2
    Check the streak
    Drag the specimen across an unglazed porcelain plate. Streak: yellow-brown.
  • 3
    Read the luster
    Hold the specimen under a strong light. Luster: submetallic.
  • 4
    Match the color range
    Compare against the expected color range: dark brown, brownish yellow, brownish black, dark red.
  • 5
    Look at form & habit
    Crystal system: cubic. Typical habit: dodecahedral crystals.

Often confused with

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

Arsenopyrite mineral
mineral
Arsenopyrite
Mohs 5.5-6

How to tell apart: Streak differs, so Cafarsite leaves yellow-brown, Arsenopyrite leaves black; luster reads submetallic on Cafarsite and metallic on Arsenopyrite.

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Often found alongside cafarsite

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

All properties

Chemical formula
(Ca,Na,□)₁₉Ti₈Fe₄Fe₄(AsO₃)₂₈F
Mohs hardness
5.5-6
Density
3.90 g/cm³
Colors
Dark brownBrownish yellowBrownish blackDark red
Streak
Yellow-brown
Luster
Submetallic
Transparency
Opaque to translucent in thin fragments
Crystal system
Cubic
Crystal habit
Dodecahedral crystals
Cleavage
None
Rarity
Rare
Uses
Collector
Host rock
On cleft faces in orthogneiss (Cherbadung, Switzerland)

Where rockhounds find cafarsite

Classic worldwide localities

  • East flank of Pizzo Cervandone, Alpe Devero, Val d’Aosta, Piedmont, Italy
  • Hemlo gold mine, Ontario, Canada

Field-hunting tip

Where it forms: On cleft faces in orthogneiss (Cherbadung, Switzerland). If you start seeing asbecasite, gasparite-, chernovite in float, you are in the right ground. Typical habit: dodecahedral crystals. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cafarsite?+
Mohs hardness is 5.5-6. Luster: submetallic. The streak is yellow-brown. Common colors include dark brown, brownish yellow, brownish black, dark red.
Where is cafarsite found?+
Notable localities include East flank of Pizzo Cervandone, Alpe Devero, Val d’Aosta, Piedmont, Italy; Hemlo gold mine, Ontario, Canada.
Is cafarsite safe to handle?+
Cafarsite contains arsenic and calls for real care. Contains arsenic. Handle with care, avoid inhalation of dust, and wash hands thoroughly after handling.
What rocks look like cafarsite?+
Cafarsite is most often confused with Arsenopyrite. A quick hardness test and a streak check separate the look-alikes faster than color alone.
What minerals are found with cafarsite?+
Cafarsite commonly co-occurs with Asbecasite, Gasparite-, Chernovite, Synchysite. Spotting any of these in float or country rock is a useful trip signal.
What kind of rock does cafarsite form in?+
Where it forms: On cleft faces in orthogneiss (Cherbadung, Switzerland). Working float back to the host body is the standard way to chase a fresh occurrence.
What is cafarsite used for?+
Cafarsite is used in collector.

Find cafarsite on the map

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