Yeomanite, Pb2O(OH)Cl, a new chain-structured Pb oxychloride from Merehead Quarry, Somerset, England

Abstract

AbstractYeomanite, Pb2O(OH)Cl, is a new Pb-oxychloride found in the manganese pod mineral assemblage at Merehead (Torr Works) Quarry, near Cranmore, Somerset, England. Yeomanite is named in joint recognition of Mrs Angela Yeoman (1931–) and her company, Foster Yeoman, who operated Merehead Quarry for aggregate until 2006. The mineral is normally white, occasionally grey, with a white streak and a vitreous to transparent lustre. Invariably intimately associated with mendipite, yeomanite appears to be formed of small, twisted, rope-like fibres growing from the end of columnar mendipite masses, forming loose mats and strands resembling asbestos. Individual fibres are generally <8 mm long, but exceptionally may reach up to 15 mm. There is a perfect cleavage parallel to the long axis of the fibres but this is masked by the fibrous nature, especially as individual fibres break easily. The Dcalc for the ideal formula is 7.303 g/cm3. The mean RI in air at 589 nm is 2.27. The eight strongest reflections in the powder X-ray diffraction pattern [(d in Å) (Intensity) (hkl)] are: 2.880(100)(113); 2.802(78)(006); 3.293(61)(200); 3.770(32)(011); 2.166(22)(206); 1.662(19)(119); 2.050(18)(303); 3.054(17)(105) Yeomanite is orthorhombic, Pnma, a = 6.585(10), b = 3.855(6), c = 17.26(1) Å, V = 438(1) Å3, Z = 4. Yeomanite is a new example of the growing family of lead oxychloride minerals that have a structure based upon oxocentred OPb4 tetrahedra, which, in this mineral, jointly with OHPb3 triangles, form [O(OH)Pb2]+ chains similar to those observed in synthetic Pb2O(OH)I. Yeomanite is structurally related to sidpietersite, penfieldite and laurionite.