Ferrostalderite is a rare member of the tetrahedrite group characterized by its iron-rich composition. It is typically found in rare, complex hydrothermal deposits such as those in the Binn Valley, usually appearing as small, dark tetrahedral crystals.

Hardness

3.5-4

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareTetrahedrite Group family

Ferrostalderite

Hardness: 3.5-4
Luster: Metallic
Streak: Black
Transparency: Opaque

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Is this ferrostalderite?

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 ferrostalderite with a known reference. Ferrostalderite sits at Mohs 3.5-4, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Ferrostalderite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Ferrostalderite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: black, gray.
5
Look at form & habit
Crystal system: trigonal. Typical habit: tetrahedral crystals, massive.

Often confused with

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

Often found alongside ferrostalderite

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

All properties

Chemical formula: Cu₆Fe₃Sb₄S₁₃
Mohs hardness: 3.5-4
Density: 4.9-5.1 g/cm³
Colors: Black Gray
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Trigonal
Crystal habit: Tetrahedral Crystals, Massive
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Veins, Metamorphic Dolomite
Typical price: $50-300 per specimen

Where rockhounds find ferrostalderite

Classic worldwide localities

Lengenbach Quarry, Binn Valley, Switzerland
Aglerite locality, USA

Field-hunting tip

Look in hydrothermal veins, metamorphic dolomite country, the host setting where ferrostalderite typically forms. If you start seeing pyrite, sphalerite, dolomite in float, you are in the right ground. Field specimens usually show a tetrahedral crystals, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ferrostalderite?+

Mohs hardness is 3.5-4. It typically shows a metallic luster. The streak is black. Common colors include black, gray.

Where is ferrostalderite found?+

Notable localities include Lengenbach Quarry, Binn Valley, Switzerland; Aglerite locality, USA.

How much is ferrostalderite worth?+

Typical asking prices fall in the range of $50-300 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

Is ferrostalderite safe to handle?+

It contains toxic constituents. Contains copper, iron, antimony, and sulfur. Wash hands thoroughly after handling and avoid inhaling dust while trimming or polishing. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like ferrostalderite?+

Ferrostalderite is most often confused with Tetrahedrite-(Fe). A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with ferrostalderite?+

Ferrostalderite commonly co-occurs with Pyrite, Sphalerite, Dolomite, Realgar. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ferrostalderite form in?+

Ferrostalderite typically forms in hydrothermal veins, metamorphic dolomite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ferrostalderite used for?+

Ferrostalderite is used in collector.

Find ferrostalderite on the map

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