Peterchinite, the Zn-dominant member of the chlorophoenicite group from the Franklin Mine, Sussex County, New Jersey, USA

Peterchinite (IMA2023–050), Zn3(OH)2[Zn2(AsO3OH)(OH)6], is a new member of the chlorophoenicite group from the Franklin mine, Franklin Mining District, Sussex County, New Jersey, USA. It occurs as finely matted, tightly intergrown sprays of colorless acicular crystals up to ∼100 μm long, associated with hodgkinsonite, baryte, and zincite in franklinite–willemite–calcite ore, and is the Zn-dominant analogue of chlorophoenicite and magnesiochlorophoenicite. Crystals are transparent to translucent with a vitreous luster and white streak, are non-fluorescent, brittle and very soft (Mohs hardness ca. 2) with irregular fracture. The calculated density is 3.534 g·cm–3 (empirical formula). Peterchinite is biaxial; the refractive index measured parallel to the elongation direction [010] is 1.680(3), assumed to be β. Electron-microprobe analysis, with H calculated from the structure to achieve charge balance, gives the empirical formula (Zn1.34Mg1.20Mn0.45Ca0.01)3.00(OH)2[Zn2((As0.97Si0.02)O2.93(OH)1.07)(OH)6]. The five strongest powder X-ray diffraction lines [dobs Å(I)(hkl)] are 6.88(46)(001,–201), 3.704(55)(–601), 3.085(38)(202), 2.593(100)(510), and 1.744(40)(–11·1·1). Peterchinite is monoclinic, space group C2/m, with a = 22.953(12), b = 3.210(12), c = 7.278(12) Å, β = 106.426(12)°, V = 514(2) Å3, and Z = 2. It is isostructural with chlorophoenicite based on the nearly identical PXRD and Raman spectra. Peterchinite is named for Peter Chin, a long-time collector and student of the mineralogy of Franklin and Sterling Hill.