Ferroselite is a rare iron selenide mineral typically found in hydrothermal uranium-rich deposits. It is most easily identified by its distinct metallic luster and association with other selenium minerals like clausthalite, often occurring as fine-grained, radiating, or acicular crystals.

Hardness

6-6.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrare

Ferroselite

Hardness: 6-6.5
Luster: Metallic
Streak: Black
Transparency: Opaque

Is this ferroselite?

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 ferroselite with a known reference. Ferroselite sits at Mohs 6-6.5, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Ferroselite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Ferroselite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: white, gray.
5
Look at form & habit
Crystal system: orthorhombic. Typical habit: acicular or fibrous crystals, massive aggregates, granular.

Often confused with

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

mineral

Pyrite

Mohs 6-6.5

How to tell apart: Streak differs, so Ferroselite leaves black, Pyrite leaves greenish-black to brownish-black.

Compare →

Often found alongside ferroselite

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

All properties

Chemical formula: FeSe₂
Mohs hardness: 6-6.5
Density: 6.8 g/cm³
Colors: White Gray
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Orthorhombic
Crystal habit: Acicular or Fibrous Crystals, Massive Aggregates, Granular
Cleavage: Distinct On {101}
Rarity: Rare
Uses: Collector
Host rock: Hydrothermal Veins, Uranium Deposits

Where rockhounds find ferroselite

Classic worldwide localities

Udykon River, Russia
Clausthal-Zellerfeld, Germany
Sierra de Umango, Argentina
Temple Mountain, USA

Field-hunting tip

Look in hydrothermal veins, uranium deposits country, the host setting where ferroselite typically forms. If you start seeing clausthalite, uraninite, calcite in float, you are in the right ground. Field specimens usually show a acicular or fibrous crystals, massive aggregates, granular habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify ferroselite?+

Mohs hardness is 6-6.5. It typically shows a metallic luster. The streak is black. Common colors include white, gray.

Where is ferroselite found?+

Notable localities include Udykon River, Russia; Clausthal-Zellerfeld, Germany; Sierra de Umango, Argentina; Temple Mountain, USA.

Is ferroselite safe to handle?+

It contains toxic constituents. Contains selenium, which is toxic if inhaled or ingested. Wash hands thoroughly after handling and avoid creating dust or powder when breaking or sawing specimens. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like ferroselite?+

Ferroselite is most often confused with Pyrite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with ferroselite?+

Ferroselite commonly co-occurs with Clausthalite, Uraninite, Calcite, Pyrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does ferroselite form in?+

Ferroselite typically forms in hydrothermal veins, uranium deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is ferroselite used for?+

Ferroselite is used in collector.

Find ferroselite on the map

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