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

2.5-3

Mohs

Luster

Metallic

Streak

Black

Transparency

Opaque

mineralrareTetragonal copper-iron sulfides family

Thalcusite

Hardness: 2.5-3
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 2.5-3, 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: bronze, black.
5
Look at form & habit
Crystal system: tetragonal. Typical habit: bladed.

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, so 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: 2.5-3
Density: 6.15 g/cm³
Colors: Bronze Black
Streak: Black
Luster: Metallic
Transparency: Opaque
Crystal system: Tetragonal
Crystal habit: Bladed
Cleavage: Parallel to grain elongation
Rarity: Rare
Uses: Collector
Host rock: In base-metal sulfide deposits and hyperalkalic massifs

Where rockhounds find thalcusite

Classic worldwide localities

Majak mine, Talnakh area, Noril’sk region, western Siberia (type locality), Russia
Murun massif, southwest of Olekminsk, Sakha, Russia
Kangerdluarssuk Fjord and at Nakkaalaaq Mountain, southern Greenland
Rajpura-Dariba polymetallic deposit, Rajasthan, India
Mont Saint-Hilaire, Quebec, Canada

Field-hunting tip

Where it forms: In base-metal sulfide deposits and hyperalkalic massifs. If you start seeing altaite, galena, sphalerite in float, you are in the right ground. Typical habit: bladed. Train your eye for that shape before scanning the outcrop.

Common questions

How do you identify thalcusite?+

Mohs hardness is 2.5-3. Luster: metallic. The streak is black. Common colors include bronze, black.

Where is thalcusite found?+

Notable localities include Majak mine, Talnakh area, Noril’sk region, western Siberia (type locality), Russia; Murun massif, southwest of Olekminsk, Sakha, Russia; Kangerdluarssuk Fjord and at Nakkaalaaq Mountain, southern Greenland; Rajpura-Dariba polymetallic deposit, Rajasthan, India; Mont Saint-Hilaire, Quebec, Canada.

Is thalcusite safe to handle?+

Thalcusite contains copper and thallium and calls for real care. Contains thallium, which is highly toxic. Handle with care and avoid inhalation of dust or ingestion; wash hands thoroughly after handling.

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 Altaite, Galena, Sphalerite, Djerfisherite, Pentlandite, Cubanite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does thalcusite form in?+

Where it forms: In base-metal sulfide deposits and hyperalkalic massifs. 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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