VAESITE
Vaesite is a very rare sulfide, occurring in some very specific parageneses. It is not an ore.
It is classified in the Pyrite Group. It is isostructural with cattierite, with which it forms a series. It may contain Co and Fe, and there is a variety with Se.
Vaesite crystals appear as cubes and octahedrons, and can form combined forms, such as cubo-octahedrons, with smooth cube faces and rough octahedron faces with a metallic luster.
Macroscopically, vaesite can be confused with sphalerite!
1. Characteristics
Crystal system: Cubic diploidal.
Color: Black, silver gray.
Habit: Crystals such as cubes, octahedrons, or combined cubic shapes, up to 1 cm in size. Massive.
Cleavage: {001} good.
Tenacity: No information available.
Twinning: No.
Fracture: No information available.
Mohs Hardness: 4.5 – 5.5
Parting: No.
Streak: Black.
Lustre: Metallic.
Diaphaneity: Opaque.
Density (g/cm³): 4.45
2. Geology and Deposits
Vaesite can occur disseminated in dolomites, as in the type locality (Mina Menda, Lualaba, Democratic Republic of Congo).
In other occurrences (Germany) it forms as an alteration product of As-deficient skutterudite-(Ni).
3. Mineral Associations
It is associated with common gangue minerals such as carbonates (calcite, dolomite).
Its association with millerite is very common.
It occurs with common sulfides such as pyrite, marcasite, and molybdenite.
With various Cu sulfides such as bornite, chalcocite, digenite, covellite, and chalcopyrite.
With Se minerals such as trogtalite, krut’aite, penroseite, and clausthalite.
Also with other sulfides (polydymite, linnaeite), sulfates (jamborite), phyllosilicates (nepouite), sulfosalts (arsenohauchecornite), arsenates (eskutterudite (Ni), niqueline), and oxides (uraninite).
It never occurs with cattierite in the same vein.
4. Transmitted Light Microscopy
This does not apply, as vaesite is completely opaque.
5. Reflected Light Microscopy
Sample preparation: There is no information on the behavior of vaesite during polishing.
PLANE POLARIZED LIGHT – PPL
Reflection color: Gray with a subtle violet hue.
Compared to the color of sphalerite, the color of vaesite is very similar, but somewhat lighter.
Compared to the color of tennantite, the color of vaesite is darker.
Pleochroism: No.
Reflectivity: 31,55%
With Co: 31.8%, with Cu: 33,2%, with Se: 33,8%
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Isotropic.
Sometimes with weak anisotropy in dark gray-brown.
Internal reflections: No.
May be confused with: galena and gersdorffite are related due to their perfect cubic cleavage, but their reflection color is different.
General Characteristics:
Grain shape: Vaesite occurs in cubes, octahedrons, and combined cubic forms. It can exhibit a granular or massive habit.
Cleavage can be very well developed, including along two perpendicular directions (cubic cleavage, similar to gersdorffite cleavage, can be as well developed as galena cleavage).
Zoning is likely to occur, as in pyrite-(Ni) (“bravoite”).
Substitutions 1: Vaesite can replace linnaeite and pyrite.
Substitutions 2: Vaesite is replaced by millerite, polydymite, native gold, and siegenite.
