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

5-6

Mohs

Luster

Resinous

Streak

Yellow-brown

Transparency

Translucent

mineralrarenull family

Cafarsite

Hardness: 5-6
Luster: Resinous
Streak: Yellow-brown
Transparency: Translucent

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 5-6 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Cafarsite leaves a yellow-brown streak.
3
Read the luster
Hold the specimen under a strong light. Cafarsite typically shows a resinous luster.
4
Match the color range
Compare against the expected color range: dark brown, black, reddish-brown.
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.

mineral

Arsenopyrite

Mohs 5.5-6

How to tell apart: Streak differs — Cafarsite leaves yellow-brown, Arsenopyrite leaves black; luster reads resinous 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: Ca₈(Ti,Fe³⁺,Mn)₆(AsO₃)₁₂·4H₂O
Mohs hardness: 5-6
Density: 4.7-4.8 g/cm³
Colors: Dark Brown Black Reddish-brown
Streak: Yellow-brown
Luster: Resinous
Transparency: Translucent
Crystal system: Cubic
Crystal habit: Dodecahedral Crystals
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Dolomitic Marble
Typical price: $50-500 depending on crystal size and quality

Where rockhounds find cafarsite

Classic worldwide localities

Binntal, Valais, Switzerland

Field-hunting tip

Look in dolomitic marble country — that is the host setting where cafarsite typically forms. If you start seeing dolomite, realgar, sperrylite in float, you are in the right ground. Field specimens usually show a dodecahedral crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify cafarsite?+

Mohs hardness is 5-6. It typically shows a resinous luster. The streak is yellow-brown. Common colors include dark brown, black, reddish-brown.

Where is cafarsite found?+

Notable localities include Binntal, Valais, Switzerland.

How much is cafarsite worth?+

Typical asking prices fall in the range of $50-500 depending on crystal size and quality. Quality, size, and provenance can move individual specimens well outside that range.

Is cafarsite safe to handle?+

It contains toxic constituents. Contains arsenic. Handle with care, avoid inhalation of dust, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

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 Dolomite, Realgar, Sperrylite, Anatase. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does cafarsite form in?+

Cafarsite typically forms in dolomitic marble. 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

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.