EMPLECTITE
Emplectite – CuBiS2 – is a relatively rare sulfide found in complex sulfide ores. It is not a significant ore mineral.
1. Characteristics
Crystal system: Orthorhombic dipyramidal.
Color: Tin-white to grayish. A fresh fracture has a yellow hue, darkening to shades of green.
Habit: Small prismatic crystals, flattened on {010}, fibrous, acicular.
Cleavage: {010} perfect, {001} distinct. Striations paralell to [001]
Tenacity: Brittle.
Twinning: Contact twins are possible.
Fracture: Irregular to conchoidal.
Mohs Hardness: 2
Parting: No.
Streak: No information available.
Lustre: Metallic.
Diaphaneity: Opaque.
Density (g/cm³): 6.38
2. Geology and Deposits
Emplectite occurs primarily in moderate-temperature hydrothermal veins associated with sulfides and sulfosalts of the Bi-Cu-As-Co-Ag-Ni association, especially in Bi-enriched zones.
It also forms in Bi-rich zones of contact-metasomatic deposits (skarns).
3. Mineral Associations
It is associated with common hydrothermal vein gangue minerals: quartz, barite, fluorite, and carbonates (calcite, siderite).
It also occurs with common sulfides such as pyrite, sphalerite, and molybdenite.
Minerals specific to the paragenesis include:
– Bi minerals (native bismuth, bismutite, petitjeanite, beyerite, laitakarite, wittichenite), and
– Cu minerals (chalcopyrite, brochantite, chalcophyllite, mrázekite, tetrahedrite-tennantite, luzonite-famatinite, nekrasovite).
4. Transmitted Light Microscopy
Not applicable, as emplectite is completely opaque.
5. Reflected Light Microscopy
Sample preparation: Due to its low hardness, polishing emplectite is relatively simple. Its polishing hardness is higher than that of native bismuth and slightly lower than that of bismuthinite.
PLANE POLARIZED LIGHT – PPL
Reflection color: Light yellow or yellowish-gray, sometimes with a brown tint; it resembles chalcopyrite.
Compared to the color of chalcopyrite, the color of emplectite is whiter.
Compared to the color of galena, the color of emplectite has a brownish-cream hue.
Compared to the color of bismuthinite, the color of emplectite is slightly less bright and more yellowish.
Pleochroism: Very weak, visible only at intergranular boundaries.
Reflectivity: 37.23 – 38.44%
Bireflectance: Weak.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Strong anisotropy between turquoise-toned gray and dark brown. Other sources record colors ranging from brown to bluish, as well as dark violet. The colors shift with even the slightest rotation of the stage.
Internal reflections: No.
May be confused with: Several other minerals. Identifying emplectite is difficult both macroscopically and under the microscope. The situation is further complicated in the presence of native bismuth, as many minerals in the paragenesis appear to have a bluish tint when compared to native bismuth.
Bismuthinite is similar but exhibits stronger pleochroism and lighter-colored anisotropy; additionally, cleavage parallel to the elongation is often visible and serves as a diagnostic feature.
Wittichenite generally forms rounded grains, lacks cleavage, and exhibits weaker pleochroism and anisotropy.
Annivite is significantly harder, isotropic, and shows much lower reflectivity.
General Characteristics:
Grain shape: Emplectite generally occurs as acicular to fibrous euhedral crystals; it also appears in granular aggregates.
Cleavage parallel to (001) may be visible (i.e., perpendicular to the elongation).
Twinning has been observed only in polished sections, not in macroscopic crystals. It is relatively common, with straight boundaries, and is not lamellar.
Substitutions 1: Emplectite replaces chalcopyrite, wittichenite, annivite, and others.
Substitutions 2: Emplectite is replaced by bismuthinite, covellite, and Bi-tellurides.
Inclusions of native bismuth may occur.
Intergrowths with bismuthinite may occur.
