Thalfenisite is a rare thallium-bearing sulfide mineral typically found in complex nickel-copper ore deposits. It usually occurs as microscopic grains embedded within other sulfide minerals, making it a challenging find for even advanced collectors.

Hardness

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrare

Thalfenisite

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

Is this thalfenisite?

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 thalfenisite with a known reference. Thalfenisite sits at Mohs 3, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Thalfenisite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Thalfenisite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: steel-gray, black.
5
Look at form & habit
Crystal system: cubic. Typical habit: anhedral grains, interstitial masses.

Often confused with

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

Often found alongside thalfenisite

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

All properties

Chemical formula: Tl₆(Fe,Ni,Cu)₂₅S₂₆
Mohs hardness: 3
Density: 6.12 g/cm³
Colors: Steel-gray Black
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Cubic
Crystal habit: Anhedral Grains, Interstitial Masses
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Copper-nickel Sulfide Deposits in Mafic Igneous Rocks
Typical price: $100-500 for micro-mounts

Where rockhounds find thalfenisite

Classic worldwide localities

Talnakh deposit, Norilsk, Russia

Field-hunting tip

Look in copper-nickel sulfide deposits in mafic igneous rocks country, the host setting where thalfenisite typically forms. If you start seeing pentlandite, chalcopyrite, cubanite in float, you are in the right ground. Field specimens usually show a anhedral grains, interstitial masses habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thalfenisite?+

Mohs hardness is 3. It typically shows a metallic luster. The streak is black. Common colors include steel-gray, black.

Where is thalfenisite found?+

Notable localities include Talnakh deposit, Norilsk, Russia.

How much is thalfenisite worth?+

Typical asking prices fall in the range of $100-500 for micro-mounts. Quality, size, and provenance can move individual specimens well outside that range.

Is thalfenisite safe to handle?+

It contains toxic constituents. Contains thallium, a highly toxic heavy metal. Handle with gloves, avoid inhalation of dust, and wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like thalfenisite?+

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

What minerals are found with thalfenisite?+

Thalfenisite commonly co-occurs with Pentlandite, Chalcopyrite, Cubanite, Galena. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does thalfenisite form in?+

Thalfenisite typically forms in copper-nickel sulfide deposits in mafic igneous rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thalfenisite used for?+

Thalfenisite is used in collector.

Find thalfenisite on the map

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