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Thalfenisite

Discovered in 1979; IMA status: Valid (IMA approved 1979)

Chemistry

Chemical Formula:

Tl₆(Fe,Ni,Cu)₂₅S₂₆Cl

Thallium Iron Nickel Copper Sulfide Chloride (halide-sulfide or chlor-sulfide)

Molecular Weight:

3,510.71 gm

Composition:

Thallium

34.93 %

Tl

Iron

31.82 %

Fe

Copper

1.81 %

Cu

Nickel

6.69 %

Ni

Sulfur

23.75 %

S

Chlorine

1.01 %

Cl

100.00 %

Classification

Mineral Classification:

Sulfides

Strunz 8th Ed. ID:

2/F.06-20

Nickel-Strunz 10th Ed. ID:

2.FC.05

2 : SULFIDES and SULFOSALTS (sulfides, selenides, tellurides; arsenides, antimonides, bismuthides; sulfarsenites, sulfantimonites, sulfbismuthites, etc.)
F : Sulfides of arsenic, alkalies; sulfides with halide, oxide, hydroxide, H₂O
C : With Cl, Br, I (halide-sulfides)

Related to:

Djerfisherite Group. The thallium analog of Djerfisherite.

Members of Group:

Djerfisherite Group: Cu-djerfisherite, Djerfisherite, Owensite, Thalfenisite 

Varieties:

None

Synonyms:

IMA1979-018

Crystal Data

Crystallography:

Isometric - Hexoctahedral

Crystal Habit:

As grains, to 5 - 30 μm, in aggregates. These are microscopic crystals visible only with a microscope.

Twinning:

None

Physical Properties

Cleavage:

None

Fracture:

n/a

Tenacity:

Brittle

Mohs Hardness:

1.0 - 1.5; VHN = 130-164 (100 g load)

Density:

5.26 calculated (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Brown, bronze brown, greenish brown. Brown in reflected light, dark brown in oil

Transparency:

Opaque

Luster:

Metallic

Refractive Index:

R: (400) 24.2, (440) 23.6, (480) 23.6, (520) 24.3, (560) 25.6, (600) 27.3, (640) 28.7, (700) 30.3

Birefringence:

0.000 (opaque)

Dispersion:

n/a

Pleochroism:

None

Anisotrophism:

In reflected light: brown

Occurances

Geological Setting:

In pentlandite-galena-chalcopyrite ores, localized at the contact of chalcopyrite and galena and included in pentlandite.

Common Associations:

Pentlandite, Galena, Chalcopyrite

Common Impurities:

K

Type Locality:

Oktyabr'skoe Cu-Ni deposit (Oktyabr'skoye; Oktyabr'sky), Talnakh Cu-Ni Deposit, Noril'sk, Putoran Plateau, Taimyr Peninsula, Taymyrskiy Autonomous Okrug, Eastern-Siberian Region, Russia

Year Discovered:

1979

View mineral photos:

Thalfenisite mineral photos and locations

Unusual Gem Categories

Metallic Gems

More Information

Mindat.org
Webmineral.com

Thalfenisite is an extremely rare thallium chlor-sulfide mineral that is found as tiny (5 - 30 μm) subhedral to euhedral grains, typically triangular in cross-section, enclosed within chalcopyrite in pentlandite-galena-chalcopyrite ore aggregates. The crystals are visible only with a microscope. The "cabochon" in the picture above is a scientific specimen consisting of a 4.6mm sample in an analytical mount. The sample is a polished chalcopyrite crystal containing a microscopic grain of Thalfenisite. The sample has been analysed using a scanning electron microscope (SEM) and verified to contain Thalfenisite. Thalfenisite is a bronze brown, opaque, soft mineral with a Mohs hardness of 1 - 1.5 and metallic luster. Thalfenisite is very unusual in that it has an extremely high molecular weight of 3,510.71 gm. Compare this to the molecular weights of Diamond (12.01 gm), Quartz (60.08 gm) and Cerussite (267.21 gm).

Thalfenisite's name reflects its composition of THALlium, FErrum for iron, NIckel and Sulfur (Thal-fe-ni-s-ite). It was discovered in 1979 by N. S. Rudashevsky, A. M. Karpenkov, G. S. Shipova, N. N. Shishkin and V. A. Ryabikin at the Oktyabr'skoe Cu-Ni deposit, Noril'sk, Putoran Plateau, Taimyr Peninsula, Taymyrskiy Autonomous Okrug, Eastern-Siberian Region, Russia. This is the only occurrence of Thalfenisite known to date.

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