Sederholmite is a rare nickel selenide that typically occurs as tiny, metallic, hexagonal plates or grains within hydrothermal veins. It is most often identified by its association with other rare selenium-bearing minerals in complex ore deposits. Collectors primarily seek it as an obscure end-member in mineralogical suites.

Hardness

3-3.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareMillerite Group family

Sederholmite

Hardness: 3-3.5
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this sederholmite?

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 sederholmite with a known reference. Sederholmite sits at Mohs 3-3.5 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Sederholmite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Sederholmite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: bronze, pale brass-yellow.
5
Look at form & habit
Crystal system: hexagonal. Typical habit: hexagonal plates, granular, massive.

Often confused with

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

mineral

Millerite

Mohs 3-3.5

How to tell apart: Streak differs — Sederholmite leaves black, Millerite leaves bright greenish-black.

How to tell apart: Sederholmite is noticeably harder (Mohs 3-3.5 vs. 1-2).

Compare →

Often found alongside sederholmite

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

All properties

Chemical formula: β-NiSe
Mohs hardness: 3-3.5
Density: 5.65 g/cm³
Colors: Bronze Pale Brass-yellow
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Hexagonal
Crystal habit: Hexagonal Plates, Granular, Massive
Cleavage: Distinct On Basal Plane
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Selenide Veins
Typical price: $50-300 per specimen

Where rockhounds find sederholmite

Classic worldwide localities

Uran mine, Czech Republic
Trogtal quarry, Germany
Clausthal-Zellerfeld, Germany

Field-hunting tip

Look in hydrothermal selenide veins country — that is the host setting where sederholmite typically forms. If you start seeing clausthalite, tiemannite, berzelianite in float, you are in the right ground. Field specimens usually show a hexagonal plates, granular, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify sederholmite?+

Mohs hardness is 3-3.5. It typically shows a metallic luster. The streak is black. Common colors include bronze, pale brass-yellow.

Where is sederholmite found?+

Notable localities include Uran mine, Czech Republic; Trogtal quarry, Germany; Clausthal-Zellerfeld, Germany.

How much is sederholmite 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 sederholmite safe to handle?+

It contains toxic constituents. Contains nickel and selenium, both of which are toxic if ingested or inhaled as dust; wash hands thoroughly after handling and avoid creating dust. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like sederholmite?+

Sederholmite is most often confused with Millerite, Haapalaite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with sederholmite?+

Sederholmite commonly co-occurs with Clausthalite, Tiemannite, Berzelianite, Umangite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does sederholmite form in?+

Sederholmite typically forms in hydrothermal selenide veins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is sederholmite used for?+

Sederholmite is used in collector.

Find sederholmite on the map

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