Metaheimite (IMA 2023-020a), PbCu2(AsO4)(OH)3, has been identified as a new secondary mineral at the Grosses Chalttal deposit, Mürtschenalp district, Glarus, Switzerland. It forms radial aggregates of blade-like crystals of light blue to turquoise blue colour. Metaheimite has a light blue streak and vitreous to silky lustre. Its calculated density is 5.47 g cm–3. The empirical chemical formula based on seven anions per formula unit is (Pb0.96Ca0.03)Cu1.98(As1.01O4)(OH)3. Metaheimite is pseudo-orthorhombic, with monoclinic symmetry, space group P21/n and unit cell parameters a = 5.8347(4), b = 7.7528(6), c = 13.8899(9) Å, β = 90.018(3)°, V = 628.31(8) Å3 and Z = 4. The five strongest lines in the calculated powder diffraction pattern are (d in Å(I)hkl) as follows: 6.945(100)002, 3.870(75)112, 3.169(78)014, 3.145(99)121 and 2.615(81)015. The crystal structure, refined to Robs = 6.13% for 1393 reflections with I > 3σ(I), consists of layers similar to those occurring in heimite, PbCu2(AsO4)(OH)3·2H2O, but with 6+2 coordinated Pb2+. The lack of water molecules in metaheimite causes different interlayer hydrogen bonding and consequently, different layer stacking order as compared to that in heimite. In metaheimite, Cu2+ therefore occurs in a square-pyramidal coordination by five oxygen atoms. Hydrous species in metaheimite have been examined by Raman and by infrared spectroscopy. Metaheimite is structurally related to duftite, PbCu(AsO4)(OH) and may be considered a transitional state between heimite and duftite.

Duftite, PbCu(AsO4)(OH) is orthorhombic, space group P212121 with a = 7.768(1), b = 9. 211(1), c = 5.999(1) Å, Z = 4; the structure has been refined to R = 4.6% and Rw = 6.5% using 640 observed reflections [F> 2σ(F)]. The structure consists of chains of edge-sharing CuO6 ‘octahedra’, parallel to c; which are linked via AsO4 tetrahedra and Pb atoms in distorted square antiprismatic co-ordination to form a three dimensional network. The CuO6 ‘octahedra’ show Jahn-Teller distortion with the elongation running approximately along <627>. The hydrogen bonding network in the structure was characterized using bond valence calculations. ‘β-duftite’ is an intermediate in the duftite-conichalcite series, which has a modulated structure based on the intergrowth of the two structures in domains of approximately 50 Å. The origin of the modulation is thought to be associated with displacements in the oxygen lattice and is related to the orientation of the Jahn-Teller distortion of CuO6 ‘octahedra’. Approximately half of the strips show an elongation parallel to <627> while the other strips are elongated parallel to [010]. This ordering results in an increase in the b cell repeat compared to duftite and conichalcite.

The mineral conichalcite from the western part of Bagdad mine, Bagdad, Eureka District, Yavapai County, Arizona, USA has been characterized by electronic, near-infrared (NIR), Raman and infrared (IR) spectroscopy. Scanning electron microscopy (SEM) images show that the mineral consists of bundles of fibres. Calculations based on the results of the energy dispersive X-ray analyses on a stoichiometric basis show the substitution of arsenate by 12 wt.% of phosphate in the mineral. Raman and IR bands are assigned in terms of the fundamental modes of AsO4 3− and PO4 3−molecules and are related to the mineral structure. Near-IR reflectance spectroscopy shows the presence of adsorbed water and hydroxyl units in the mineral. The Cu(II) coordination polyhedron in conichalcite can have at best pseudo-tetragonal geometry. The crystal field and tetragonal field parameters of the Cu(II) complex were calculated and found to agree well with the values reported for known tetragonal distortion octahedral complexes.