Chenite, a new lead-copper secondary mineral, has been found on specimens from the Leadhills area, Scotland. It is associated with caledonite, linarite, leadhillite, susannite, and other species, on oxidized galena with chalcopyrite. Electron microprobe analysis yielded PbO 74.5, CuO 7.8, SO3 13.3, H2O 4.4 (by difference), sum = 100 wt. %. The empirical formula (based on 14 oxygens) is Pb3.98Cu1.17S1.98O14H5.82; the ideal formula is Pb4Cu(SO4)2(OH)6, which requires PbO 75.2, CuO 6.7, SO3 13.5, H2O 4.6, sum = 100 wt. %.

Infra-red spectroscopy showed the presence of only and OH− ions, with no H2O.

Chenite is triclinic, P1 or P̄, with a = 5.791(1), b = 7.940(1), c = 7.976(1) Å, α = 112.02(1), β = 97.73(1), γ = 100.45(1)°, V = 326.0 Å3, Z = 1. The strongest lines in the X-ray powder diffraction pattern (d, I/Io, hkl) are: 5.55, 7, 100; 4.32, 6, 11; 3.60, 10 002; 3.41, 9, 10; 3.30, 5, 02; 3.00, 5, 111; 2.80, 7, 12; 2.07, 6, 211/21/13; 1.778, 5, 3/23.

Chenite forms minute, singly terminated, transparent to translucent sky-blue crystals from 0.1 to over 1 mm long, elongated approximately [032]. Twenty different forms (pinacoids) have been identified on the four crystals studied. A good cleavage on {100}, and traces of a second on {001}, can be observed. Optically, chenite is biaxial negative, 2 V(measured) = 67±1°, 2 V(calc.) = 68° (Na). The refractive indices are α 1.871±0.005, β 1.909±0.005, γ 1.927±0.005 (Na). Dispersion is strong, r≫v. The mineral is weakly pleochroic. H (Mohs) ∼ 2½. D = 5.98, and calculated Dx = 6.044 g cm−3.

Published electron microprobe analyses of mattheddleite, a lead sulpho-silicate apatite from Leadhills, Scotland, have 9–13% IV site deficiencies. However, galena was used as a standard for S, which suggested that low S resulted from a shift in the S-Kα peak. Wavelength scans with a PET crystal show that the S-Kα peak is shifted down by 0.0026 Å for sulphates relative to sulphides. Quantitative analyses show a ∼30% increase of S in mattheddleite using a celestite standard, which fills the IV site, but with Si > S, on average Pb5S1.2Si1.8O11.7Cl0.6(OH)0.4. Direct analysis of oxygen with the electron microprobe implies that the charge imbalance engendered from the inequality of Si and S is compensated with substitution of a vacancy (□), as in Pb5S1.2Si1.8[O11.7□0.3] [Cl0.6(OH)0.4] or Pb5S1.2Si1.8[O11.7(Cl, OH)0.73]. [Cl,OH)0.7 □0.3]. Calculation of OH as l–C1 suggests the presence of both OH- and Cl-dominant mattheddleite at Leadhills, but direct analysis of H is needed to confirm the dominance of OH in the channel site. Wavelength-dispersive analyses of S in apatite and other sulphates must be undertaken with sulphate standards: use of sulphide standards yields a negative error on the order of 10–20% in the resultant S concentration. Reactions of mattheddleite with other Pb minerals at Leadhills show that their stability depends on fluid composition as well as pressure and temperature. An X-ray map of Cl shows complex zoning between Cl-poor and Cl-rich mattheddleite, recording rapid changes in the fluid chemistry during late-stage hydrothermal processes at Leadhills.