Thalcusite is a very rare copper-iron-thallium sulfide mineral typically found in massive, non-descript grains within base metal sulfide ores. It is primarily known from the type locality in the Noril'sk region of Russia, where it occurs alongside other sulfide minerals.

Hardness

3.5

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareTetragonal copper-iron sulfides family

Thalcusite

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

No image

Is this thalcusite?

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 thalcusite with a known reference. Thalcusite sits at Mohs 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. Thalcusite leaves a black streak.
3
Read the luster
Hold the specimen under a strong light. Thalcusite typically shows a metallic luster.
4
Match the color range
Compare against the expected color range: bronze-yellow, brass-yellow.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: massive, anhedral grains.

Often confused with

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

mineral

Chalcopyrite

Mohs 3.5-4

How to tell apart: Streak differs — Thalcusite leaves black, Chalcopyrite leaves greenish-black.

Often found alongside thalcusite

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

All properties

Chemical formula: Cu₃Tl₂FeS₄
Mohs hardness: 3.5
Density: 5.3 g/cm³
Colors: Bronze-yellow Brass-yellow
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Tetragonal
Crystal habit: Massive, Anhedral Grains
Cleavage: None
Rarity: Rare
Uses: Collector
Host rock: Copper-nickel Sulfide Ore Deposits
Typical price: $50-300 per specimen

Where rockhounds find thalcusite

Classic worldwide localities

Talnakh deposit, Noril'sk, Russia

Field-hunting tip

Look in copper-nickel sulfide ore deposits country — that is the host setting where thalcusite typically forms. If you start seeing chalcopyrite, cubanite, bornite in float, you are in the right ground. Field specimens usually show a massive, anhedral grains habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thalcusite?+

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

Where is thalcusite found?+

Notable localities include Talnakh deposit, Noril'sk, Russia.

How much is thalcusite 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 thalcusite safe to handle?+

It contains toxic constituents. Contains thallium, which is highly toxic. Handle with care and avoid inhalation of dust or ingestion; wash hands thoroughly after handling. Handle with care, avoid grinding or breathing dust, and store separately.

What rocks look like thalcusite?+

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

What minerals are found with thalcusite?+

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

What kind of rock does thalcusite form in?+

Thalcusite typically forms in copper-nickel sulfide ore deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is thalcusite used for?+

Thalcusite is used in collector.

Find thalcusite on the map

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