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, so 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, 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.