JORDANITE
Jordanite – Pb14(As,Sb)6S23 – is a fairly rare sulfosalt that is part of complex Pb-As ores.
It forms a series with geochronite, with which it is isostructural. It is considered the high-temperature dimorph of gratonite.
1. Characteristics
Crystal system: Monoclinic prismatic.
Color: Lead gray, usually tarnished, iridescent.
Habit: Tabular to bipyramidal, pseudohexagonal. May be reniform. Crystals up to 4 cm.
Cleavage: {010} perfect.
Tenacity: Brittle.
Twinning: It exhibits common twinning by {001}, which can be lamellar by {-201}. More rarely, twinning by {-101} and by {101} is also rare. Macroscopically, recognition of the twinning can be more difficult because idiomorphic jordanite crystals typically exhibit many faces.
Fracture: Conchoidal.
Mohs Hardness: 3
Parting: On {001}.
Streak: Black.
Lustre: Metallic.
Diaphaneity: Opaque.
Density (g/cm³): 6.44
2. Geology and Deposits
Jordanite has been found in Pb-As occurrences in metamorphosed dolomites, in low-temperature epithermal veins, in quartz-gold type epithermal veins with tellurides, and also in underwater fumaroles (“black smokers”).
These are generally occurrences with high concentrations of As and very low formation temperatures.
3. Mineral Associations
Jordanite occurs with common gangue minerals such as quartz, dolomite, and barite.
It is associated with common sulfides such as pyrite, marcasite, and sphalerite.
With Cu sulfides such as chalcopyrite, bornite, digenite, chalcocite, enargite, bournonite, and covellite.
With other sulfides such as wurtzite, realgar, and orpiment.
With Ag minerals such as proustite and pyrargyrite.
It is naturally associated with other Pb sulfides and sulfosalts, with or without As. Some of these are well known such as galena, boulangerite, and tennantite. Most, however, are of restricted occurrence and require great care in their identification, such as lengenbachite, quadratite, dufrénoysite, liveingite, seligmannite, semseyite, guettardite, zinkenite, tsugaruite, hutchinsonite, meneghinite, geocronite, kirkiite, and marrite.
4. Transmitted Light Microscopy
This does not apply, as jordanite is completely opaque.
5. Reflected Light Microscopy
Sample preparation: Jordanite has a medium hardness when polished and easily acquires a fine polish. Its hardness is only slightly greater than that of galena and much less than that of sphalerite. It is slightly greater than that of semseyite.
PLANE POLARIZED LIGHT – PPL
Reflection color: White to gray, with a slight greenish tint.
Compared to galena, the color of jordanite is very similar, a little darker (more gray) and subtly greenish.
Compared to the color of baumhauerite, the color of jordanite is pinkish and lighter, not greenish like baumhauerite.
Compared to the color of gratonite, which is yellowish, the color of jordanite is whiter.
Pleochroism: Very weak, noticeable only under favorable conditions.
Reflectivity: 37.82 – 40.88%
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Anisotropy ranging from sharp and distinct, vivid and colorful, between brownish-gray and blue. It can also range from dark gray, yellowish-gray, greenish-gray, or dark brownish-gray.
Internal reflections: No.
May be confused with: Identifying jordanite is not straightforward due to the variety of environments in which it can occur.
General Characteristics:
Grain shape: rarely as idiomorphic, acicular, or reticulated crystals. Generally forms concentric or botryoidal spherical masses that show undulatory extinction and weak anisotropy. Layers of jordanite and galena may alternate. It can form “Schalenblende” (sphalerite with galena) crusts, with structures related to its origin such as gels. These crusts can reach 2 cm in thickness.
Cleavage may be present.
Regular twinning parallel to (001) may or may not be present. In some occurrences, twinning is always present, in other occurrences it is completely absent.
Substitutions 1: jordanite replaces gratonite, forming partial or total granular pseudomorphs. It also replaces pyrite.
Substitutions 2: jordanite is replaced by dufrénoysite, baumhauerite, and enargite.
Decomposition of jordanite can produce myrmekitic aggregates of seligmannite, galena, some tennantite, and native arsenic.
