BREITHAUPTITE

Breithauptite – NiSb – is a very rare sulfide (Dana), characteristic of hydrothermal Co-Ni-Ag veins. It is part of polymetallic ores, but is never the main ore mineral in the deposit.

It is classified in the Nickeline Group. It may contain Fe, Co, As, and S. There is a variety with As.

1. Characteristics

Crystal system:  Hexagonal dihexagonal bipyramidal.         

Color: Pale copper red or pale reddish-brown, soon fading to violet.     

Habit: Massive, dendritic, reniform, disseminated. Rarely in tabular or acicular crystals up to 1 mm.       

Cleavage: {0001} indicated. Some literature reports that it does not have cleavage.

Tenacity: Brittle.        

Twinning: On {10-11}.

Fracture: Subconchoidal to irregular.       

Mohs Hardness: 5.5

Parting: No.        

Streak: Reddish brown.         

Lustre: Intense metallic.          

Diaphaneity: Opaque.           

Density (g/cm³): 8.23

           

2. Geology and Deposits

Breithauptite occurs in hydrothermal calcite veins, associated with Co-Ni-Ag minerals, and may contain some As.

Deposits with breithauptite may originate at high temperatures and high pressures. In small quantities, it can also occur in galena and sphalerite veins. In some cases, it has been found in pegmatitic nickeliferous pyrrhotite and in peridotites.

 

3. Mineral Associations

It is associated with some common gangue minerals such as quartz, muscovite, and calcite.

It occurs with some common sulfides such as pyrrhotite, chalcopyrite, sphalerite, and galena.

In the specific paragenesis, with native silver, native arsenic, allargentum, dyscrasite, and sudburyite.

With Ni minerals such as gersdorffite, rammelsbergite, niqueline, maucherite, and ullmannite.

With Co minerals such as linnaeite, cobaltite, and safflorite.

With Co-Ni minerals such as eskutterudite.

With Cu minerals such as cubanite and tetrahedrite.

 

4. Transmitted Light Microscopy

This does not apply, as breithauptite is completely opaque.

5. Reflected Light Microscopy

Sample preparation:  Breithauptite exhibits high polishing hardness and achieves a very good polish, behaving approximately similarly to nickeline.

Its hardness is lower than that of safflorite, rammelsbergite, arsenopyrite, and eskuterrudite, and significantly lower than that of cobaltite.      

PLANE POLARIZED LIGHT – PPL

Reflection color: Pale copper-red (or intense pink) with a violet tint. Very characteristic and easy to observe.

Compared to the color of niqueline, the color of breithauptite is more colorful, darker, and with a violet hue.

Compared to the color of native copper, the color of breithauptite exhibits much lower reflectivity and fewer fine polishing scratches.

Pleochroism: Strong, ranging from yellow-red to light pink to pinkish-violet.      

Reflectivity: 47,82 – 54,39%.        

Bireflectance: from reddish-pink to violet.       

CROSSED POLARIZED LIGHT – XPL

Isotropy / Anisotropy: Anisotropia muito notável, com cores muito vivas e intensas: de oliva para marrom, tonalidades esverdeadas, verde intenso, cinza-azulado, verde-amarelado, verde-azulado a violeta-vermelho.        

Internal reflections: No.      

May be confused with: Few other minerals. Breithauptite is easily recognized even in unusual parageneses.

Nickeline is similar, especially in sections parallel to (0001), where the violet color does not appear, but nickeline is more orange. Nickeline exhibits weaker pleochroism and anisotropy.

Violarite is similar, but does not exhibit any type of zoning.

Freboldite is similar, but restricted to parageneses with Se.       

General Characteristics: 

Grain shape is generally anhedral granular. It can be euhedral, acicular, or tabular. Sometimes the grain size in the same sample varies greatly; they may all be anhedral.

Twinning is not present.

Cleavage is not present.

Zoning is very common, probably related to varying NiAs contents, through reflection pleochroism or by differentiated anisotropy effects: cores of more intense colors and edges of paler colors. Mainly in sections parallel to (0001) the zoning can be very evident. Sometimes the zoning is due to inclusions.

Zoning with nickeline is frequent, forming alternating bands of breithauptite and nickeline.

Inclusions of breithauptite, tiny and rounded, can occur in galena. Breithauptite inclusions can also occur in pentlandite, chromite, and safflorite.

Unmixings were not observed.

Deformations generate only cataclasis.

Substitutions: may be replaced by silver ores.

Rims of ullmannite, thin and white, may be present.

Substitutions 1: Breithauptite replaces safflorite.

Substitutions 2: Breithauptite is replaced by native silver, niquelite, Ag minerals, and safflorite.

Intergrowths of breithauptite occur with pyrrhotite.

Breithauptite 01: In PPL, breithauptite (pink with pleochroism), rammelsbergite (pure white), and calcite (dark gray) were found. The pink color of breithauptite is relatively easy to perceive in the presence of white minerals. The pleochroism is subtle and requires close attention to notice it.
Breithauptite 01: The same section as of the previous image, now in XPL. Rammelsbergite appears dark in the image, while breithauptite displays its anisotropic colors ranging from olive green to brown and bluish.
Breithauptite in XPL, showing its most common anisotropy color, which is a dark olive green. Gangue (calcite) with milky internal reflections.
Aggregate of breithauptite grains in XPL, showing grains in extinction position (very dark), olive-green colors, colors with brownish tones and a grain with a bluish tone (top right). Gangue (calcite) with milky internal reflections.