FÜLÖPPITE
Fülöppite – Pb3Sb8S15 – is an extremely rare sulfosalt that is part of polymetallic hydrothermal ores of the Ag-Pb-Sb-Zn paragenesis.
It is classified in the Plagionite Group, being very similar to plagionite.
1. Characteristics
Crystal system: Monoclinic prismatic.
Color: Lead gray.
Habit: Pyramidal, short prismatic, fibrous. May be thick tabular. Curved crystals are frequent. Crystals up to 3 mm.
Cleavage: No. Strong striations in two directions.
Tenacity: Brittle.
Twinning: No.
Fracture: Irregular.
Mohs Hardness: 2.5
Parting: No.
Streak: Reddish gray.
Lustre: Metallic
Diaphaneity: Opaque.
Density (g/cm³): 5.23
2. Geology and Deposits
Fülöppite occurs in hydrothermal veins, with sulfides and sulfosalts of the Ag-Pb-Sb-Zn association.
3. Mineral Associations
In the type locality (Kereszthegy Mine, Baia Mare, Romania), it is associated with sphalerite, dolomite, quartz, and native sulfur.
Therefore, it is associated with common gangue minerals such as quartz (including chalcedony variety), carbonates (calcite, dolomite), and fluorite.
In addition, it occurs with other Pb-Sb+-Ag sulfosalts (semseyite, zinkenite, fizélyite, andorite, freieslebenite, geocronite, boulangerite, jamesonite) and Sb minerals (stibnite, stibioconite).
Also with dawsonite, marcasite, cinnabar, and galena.
4. Transmitted Light Microscopy
This does not apply, as fülöppite is completely opaque.
5. Reflected Light Microscopy
Sample preparation: No information available.
PLANE POLARIZED LIGHT – PPL
Reflection color: Pure white. Tarnishes to steel blue or bronze.
Pleochroism: No.
Reflectivity: 31,9 – 40,1%
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Weak anisotropy in bluish-gray, may be moderate between blue-green and reddish-brown.
Internal reflections: No.
May be confused with: other associated sulfosalts.
General Characteristics:
Grain shape: occurs in groups of crystals (“clusters”) or in irregularly intergrown crystals.
Cleavage is not visible, unlike plagionite and semseyite.
