Reference:
▪ Crichton, W. & Müller, H. (2017): Centennialite, CaCu3(OH)6Cl2.nH2O, n = 0.7, a new kapellasite-like species, and a reassessment of calumetite. Mineralogical Magazine, 81, 1105-1124.
Abstract:
The new mineral centennialite (IMA 2013-110), CaCu3(OH)6Cl2·nH2O, was identified from three cotype specimens originating from the Centennial Mine, Houghton Co., Michigan, where it occurs as a secondary product, after acid water action upon supergene Cu mineralisation in association with, and essentially indivisible from, other copper-containing minerals such as calumetite and atacamite family minerals. It forms as pale to azure blue encrustations, often taking a botryoidal form. Centennialite is trigonal, P-3m1, a = 6.6606(9) Å, c = 5.8004(8) Å, V = 222.85(6) Å3, Z = 1. The strongest powder X-ray diffraction lines are: d-obs Å [I%] (hkl), 5.799 [100] (001), 2.583 [75] (201), 2.886 [51] (111), 1.665 [20] (220), 1.605 [17] (023), 1.600 [15] (221), 1.444 [11] (222). The X-ray refined structure forms a kagome net of planar coordinated CuO4 units with Jahn-Teller coordinated Cl apices to form octahedra that edge-share to in-plane adjacent and flattened CaO6 octahedra, which are centred about the lattice origin. All oxygen sites are protonated and shared between one Ca-octahedron and one CuO4 planar unit. Three protonated sites are linked, by hydrogen bonding to Cl sites, which sit on the triad axis. Each lattice has one Cl above, and one below, the Ca-Cu polyhedral plane. Consequently, the layers are stacked, along <001>, with two Cl sites between layers. In addition to this kapellasite-like topology, an extra c/2 site is identified as being variably water-hosting and extends the coordination of the Ca-site to 8- fold, akin to the body-diagonal Pb-Cu sheet in murdochite. Centennialite conforms to the description of the ‘Unidentified Cu-Ca-Cl Mineral’ noted in Heinrich’s Mineralogy of Michigan and is almost certainly identical to Erdös et al.’s (1981) supposed hexagonal basic calcium-copper hydroxychloride monohydrate. We comment upon relationships between calumetite and centennialite and propose a substructure model for a synthetic calumetite like phase that is directly related to centennialite.
▪ Crichton, W. & Müller, H. (2017): Centennialite, CaCu3(OH)6Cl2.nH2O, n = 0.7, a new kapellasite-like species, and a reassessment of calumetite. Mineralogical Magazine, 81, 1105-1124.
Abstract:
The new mineral centennialite (IMA 2013-110), CaCu3(OH)6Cl2·nH2O, was identified from three cotype specimens originating from the Centennial Mine, Houghton Co., Michigan, where it occurs as a secondary product, after acid water action upon supergene Cu mineralisation in association with, and essentially indivisible from, other copper-containing minerals such as calumetite and atacamite family minerals. It forms as pale to azure blue encrustations, often taking a botryoidal form. Centennialite is trigonal, P-3m1, a = 6.6606(9) Å, c = 5.8004(8) Å, V = 222.85(6) Å3, Z = 1. The strongest powder X-ray diffraction lines are: d-obs Å [I%] (hkl), 5.799 [100] (001), 2.583 [75] (201), 2.886 [51] (111), 1.665 [20] (220), 1.605 [17] (023), 1.600 [15] (221), 1.444 [11] (222). The X-ray refined structure forms a kagome net of planar coordinated CuO4 units with Jahn-Teller coordinated Cl apices to form octahedra that edge-share to in-plane adjacent and flattened CaO6 octahedra, which are centred about the lattice origin. All oxygen sites are protonated and shared between one Ca-octahedron and one CuO4 planar unit. Three protonated sites are linked, by hydrogen bonding to Cl sites, which sit on the triad axis. Each lattice has one Cl above, and one below, the Ca-Cu polyhedral plane. Consequently, the layers are stacked, along <001>, with two Cl sites between layers. In addition to this kapellasite-like topology, an extra c/2 site is identified as being variably water-hosting and extends the coordination of the Ca-site to 8- fold, akin to the body-diagonal Pb-Cu sheet in murdochite. Centennialite conforms to the description of the ‘Unidentified Cu-Ca-Cl Mineral’ noted in Heinrich’s Mineralogy of Michigan and is almost certainly identical to Erdös et al.’s (1981) supposed hexagonal basic calcium-copper hydroxychloride monohydrate. We comment upon relationships between calumetite and centennialite and propose a substructure model for a synthetic calumetite like phase that is directly related to centennialite.