Seinäjokite is a rare antimony-bearing member of the löllingite group characterized by its high density and metallic luster. It is typically found in small, massive grains within hydrothermal veins and often requires laboratory analysis for definitive identification due to its similarity to other iron-antimonide minerals.

Hardness

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareLöllingite Group family

Seinäjokite

Hardness: 5
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this seinäjokite?

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 seinäjokite with a known reference. Seinäjokite sits at Mohs 5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Streak: black.
3
Read the luster
Hold the specimen under a strong light. Luster: metallic.
4
Match the color range
Compare against the expected color range: gray.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: massive.

Often confused with

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

mineral

Löllingite

Mohs 5-5.5

How to tell apart: Streak differs, so Seinäjokite leaves black, Löllingite leaves grayish black.

Often found alongside seinäjokite

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

All properties

Chemical formula: FeSb₂
Mohs hardness: 5
Density: 7.938 g/cm³
Colors: Gray
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Orthorhombic
Crystal habit: Massive
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: In an antimony deposit, replacing antimony (Seinäjoki deposit, Finland)

Where rockhounds find seinäjokite

Classic worldwide localities

Seinäjoki antimony deposit, Vaasa, Finland (type locality)
Ilímaussaq intrusion, southern Greenland
Zolotaya Gora, Ural Mountains, Russia

Field-hunting tip

Where it forms: In an antimony deposit, replacing antimony (Seinäjoki deposit, Finland). If you start seeing antimony, antimonian westerveldite, breithauptite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify seinäjokite?+

Mohs hardness is 5. Luster: metallic. The streak is black. Common colors include gray.

Where is seinäjokite found?+

Notable localities include Seinäjoki antimony deposit, Vaasa, Finland (type locality); Ilímaussaq intrusion, southern Greenland; Zolotaya Gora, Ural Mountains, Russia.

Is seinäjokite safe to handle?+

Seinäjokite contains antimony. Contains antimony, a toxic heavy metal. Wash hands thoroughly after handling and avoid inhaling dust or powder.

What rocks look like seinäjokite?+

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

What minerals are found with seinäjokite?+

Seinäjokite commonly co-occurs with Antimony, Antimonian westerveldite, Breithauptite, Altaite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does seinäjokite form in?+

Where it forms: In an antimony deposit, replacing antimony (Seinäjoki deposit, Finland). Working float back to the host body is the standard way to chase a fresh occurrence.

What is seinäjokite used for?+

Seinäjokite is used in collector.

Find seinäjokite on the map

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