AIKINITE
Aikinite – PbCuBiS3 – is a rare sulfosalt, typical of Pb-Bi-Cu-Ag parageneses. It very rarely forms an ore, as in Beryozovskoye (Urals, Russia).
It is classified in the Aikinite-Bismuthinite series.
1. Characteristics
Crystal system: Orthorhombic pipyramidal.
Color: Dark lead gray. Always tarnishes to copper brown or red, sometimes to yellowish green.
Habit: Prismatic, columnar to acicular, rarely radial. Massive. Crystals up to 1 m.
Cleavage: {010} poor. Deep striations parallel to the length.
Tenacity: Very brittle.
Twinning: No.
Fracture: Irregular.
Mohs Hardness: 2 – 2.5
Parting: No.
Streak: Gray-black.
Lustre: Metallic.
Diaphaneity: Opaque.
Density (g/cm³): 7.06 – 7.08
2. Geology and Deposits
Aikinite occurs in high-temperature hydrothermal quartz veins containing gold.
It may not have been detected in other similar occurrences of Au-Bi-Pb-Cu quartz veins. It can also occur sporadically in low-temperature hydrothermal veins.
3. Mineral Associations
It is associated with common minerals such as quartz, carbonates (calcite, siderite, bismutite), micas (muscovite), and many well-known sulfides such as pyrite, pyrrhotite, chalcopyrite, enargite, bornite, galena, sphalerite, molybdenite, tennantite, tetrahedrite, bismuthinite, wittichenite, acanthite, tetradymite, and buckhornite.
With other Ag-Cu-Bi-Pb sulfosalts such as friedrichite, hammarite, neyite, jamesonite, galenobismuthite, cosalite, and bournonite.
It also occurs with native elements (gold, silver, bismuth), perite, safflorite, xenotime-(Y), bismuthite, and silicates (garnet (andradite), epidote, and dickite).
It may be associated with uraninite (pitchblende).
Alteration of aikinite produces covellite, which clusters into oriented groups.
4. Transmitted Light Microscopy
This does not apply, as aikinite is completely opaque.
5. Reflected Light Microscopy
Sample preparation: Polishing aikinite is difficult and does not yield good quality results due to its tenacity, as the mineral is extremely brittle and, in addition, has very low hardness. Since it is always associated with quartz, which is very hard, the contrast in hardness between quartz and aikinite creates a difficult-to-polish combination.
Its hardness upon polishing is very low, greater than the hardness of galena, similar to the hardness of bismuthinite, and less than the hardness of bouronnite.
PLANE POLARIZED LIGHT – PPL
Reflection color: White, with a light cream hue.
Compared to the color of galena, the color of aikinite is very similar, but distinctly more creamy.
Pleochroism: Weak. Only with oil immersion is it clearer and very typical.
Reflectivity: 45.28 – 46.52%
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Distinct anisotropy. Extinction is complete.
Internal reflections: No.
May be confused with: In some classic localities (e.g., Beryozovskoye (Urals, Russia)), the habit is so typical that its recognition is very simple. In complex ores, its identification can be difficult.
Diagnostics include, in addition to the habit, pleochroism (in oil!) and its behavior under chemical attack.
General Characteristics:
Grain shape: Aikinite crystals found in (hydrothermal) quartz consist of a large number of grains that may be completely unoriented or arranged in such a way that their boundaries are perpendicular to the major axis of the crystal.
Myrmekites of aikinite in gangue minerals may occur.
Cleavage occurs only in traces.
Fractures, very Irregular, are always present in large quantities.
Alteration of aikinite produces covellite, which forms groups of oriented crystals.
Intergrowths, occasional, occur with cosalite, galena, galenobismuthite, chalcopyrite, gold, tetradymite, tetrahedrite, and bournonite.
Substitutions 1: Aikinite replaces tetrahedrite.
Substitutions 2: Aikinite can be replaced by acanthite, native silver, and wittichenite.
Inclusions of aikinite occur in bornite, galena, and chalcopyrite.
Edges of aikinite crystals can be composed of covellite or native bismuth.
