JALPAITE
Jalpaite – Ag3CuS2 – is a very rare sulfide. With 71.71 wt% silver and 14.08 wt% copper, it fails to serve as an ore for either metal only because of its rarity.
1. Characteristics
Crystal system: Tetragonal, ditetragonal dipyramidal.
Color: Gray to dark gray, fading to dark gray, sometimes iridescent.
Habit: Coarse-grained, in foliated masses, grains within other sulfides, vein filling. Masses up to 5 cm.
Cleavage: Prismatic, good.
Tenacity: sectile, malleable.
Twinning: Lammelar.
Fracture: Subconchoidal.
Mohs Hardness: 2 – 2.5
Parting: No.
Streak: Black.
Lustre: Metallic.
Diaphaneity: Opaque.
Density (g/cm³): 6.82
2. Geology and Deposits
Jalpaite typically forms under low-temperature hydrothermal conditions.
3. Mineral Associations
It occurs associated with quartz, other gangue minerals, pyrite, and:
– silver minerals (iodargyrite, silver, acanthite),
– copper minerals (azurite, malachite, covellite, chrysocolla, tetrahedrite-tennantite),
– other silver and copper sulfides (mckinstryite, stromeyerite, polybasite, pearceite).
4. Transmitted Light Microscopy
Not applicable, as jalpaite is completely opaque.
5. Reflected Light Microscopy
Sample preparation: Polishing jalpaite presents no difficulties. It is easier to polish than chalcocite and much easier to polish than acanthite. The polishing hardness of jalpaite is lower than that of galena and approximately the same as that of acanthite.
PLANE POLARIZED LIGHT – PPL
Reflection color: Light grayish-white.
Compared to the color of acanthite, jalpaite has the same gray tone but may exhibit greenish hues.
Compared to chalcocite, jalpaite is light yellowish-brown.
Compared to galena, jalpaite is much darker and has a greenish tint.
Compared to stromeyerite, jalpaite shows a tendency toward purple.
Pleochroism: No.
Reflectivity: 29,67 – 32.12%
Bireflectance: Subtle, very weak.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Distinctive. Amidst various shades of blue-green and light green.
Internal reflections: No.
May be confused with: various other minerals of the paragenesis.
Acanthite exhibits weaker, less colorful anisotropy, but is very difficult to distinguish from jalpaite.
Stromeyerite and mckinstryite are very similar to jalpaite. Stromeyerite shows blue-violet anisotropy – unlike jalpaite – but distinguishing between them is very difficult.
Polybasite and canfieldite are very similar and easily confused with jalpaite.
General Characteristics:
Grain shape: Jalpaite occurs with granular habits and in lamellar forms.
Cleavage is not visible.
Polishing scratches are common due to low hardness.
Twinning occurs as a network of fine lamellae.
Myrmekitic intergrowths of galena and jalpaite may occur.
Intergrowths occur between jalpaite and acanthite, and between jalpaite and pearceite.
Inclusions OF jalpaite occur in galena and sphalerite.
Inclusions IN jalpaite may consist of mckinstryite.
Substitutions 1: Jalpaite replaces sphalerite, chalcopyrite, galena, and pitchblende.
Substitutions 2: Jalpaite can be replaced by silver, acanthite, and covellite.
Crusts of acanthite or silver may form around jalpaite crystals.
Cleavage filled with silver may occur in jalpaite. The cleavage is oriented parallel to the elongation of the crystals.
