ROQUESITE
Roquesite – CuInS2 – is a very rare sulfide, found in ~30 localities worldwide. It is of no importance as an ore.
It is classified in the Chalcopyrite Group, with which it is isotypic.
1. Characteristics
Crystal system: Tetragonal scalenohedral.
Color: Gray.
Habit: Very small grains (up to 0.3 mm) enclosed in bornite and chalcopyrite.
Cleavage: No information available.
Tenacity: No information available.
Twinning: Polysynthetic.
Fracture: No information available.
Mohs Hardness: 3.5 – 4
Parting: No information available.
Streak: No information available.
Lustre: Metallic.
Diaphaneity: Opaque.
Density (g/cm³): 4.78 (calculated).
2. Geology and Deposits
Roquesite occurs as microscopic inclusions in Cu sulfides (bornite and chalcopyrite) from high-temperature Sn-W-Bi-Mo-type hydrothermal veins in high-grade metamorphic rocks.
3. Mineral Associations
At the type locality (Charrier Mine, Allier, France), it is associated with chalcopyrite, chalcocite, covellite, sphalerite, and wittichenite.
Roquesite also occurs associated with other Cu minerals such as bornite, mawsonite, cubanite, löllingite, emplectite, stannoidite, idaite, and stromeyerite, as well as quartz, pyrite, arsenopyrite, magnetite, rutile, cassiterite, ferberite, native bismuth, and native silver.
4. Transmitted Light Microscopy
Not applicable, since roquesite is completely opaque. Literature states that roquesite is U(+).
5. Reflected Light Microscopy
Sample preparation: Roquesite takes a good polish, like sphalerite, though always with some scratches. Its polishing hardness is greater than that of bornite, falling between that of tetrahedrite and chalcopyrite.
PLANE POLARIZED LIGHT – PPL
Reflection color: Gray with a slight bluish tint, somewhat similar to sphalerite.
Pleochroism: No.
Reflectivity: 22.1 – 22.4
Bireflectance: No.
CROSSED POLARIZED LIGHT – XPL
Isotropy / Anisotropy: Very weak anisotropy in very dark colors.
Internal reflections: No.
May be confused with: One of the “fahlores” (tetrahedrite-tennantite and others).
General Characteristics:
Polishing scratches are persistent and partly diagnostic.
Polysynthetic twins are frequent, visible due to anisotropy.
