PARKINSONITE, (PB,MO,SQUARE)8O8CL2, A NEW MINERAL FROM MEREHEAD QUARRY, SOMERSET

Parkinsonite, ideally (Pb, Mo, square)8O8Cl2, is a new mineral from th e Merehead Quarry, Cranmore, Somerset, England. It occurs as compact c lusters or patches of red to purplish red bladed crystals, which have an adamantine lustre and a perfect {001} cleavage and occupy fractures and cavities in carbonate vughs in veins of manganese and iron oxide and hydroxide minerals. Associated minerals are mendipite, diaboleite, chloroxiphite, wulfenite, cerussite and hydrocerussite. Discrete crys tals were not found; intergrown crystalline aggregates are the usual f orm of occurrence. The maximum grain size is about 300 x 100 mum, but most grains are appreciably smaller. Parkinsonite was synthesized usin g high purity chemicals. The measured density of the synthetic materia l is 7.32 g/cm3; the calculated density is 7.39 g/cm3, the difference being due to minor impurity and slight porosity in the synthetic sampl e. Parkinsonite is translucent. Reflectance spectra were obtained in a ir and in oil. Refractive indices calculated from these (at 589 nm) ar e for R(o), 2.58, and R(e'), 2.42, i.e. uniaxial negative. VHN50 is 11 3-133 from which the calculated Mohs hardness is 2-2.5. X-ray studies show that parkinsonite is tetragonal with space group I4/mmm, I42mBAR, I4m2BAR, I4/mm, or I422 and a 3.9922(3), c 22.514(2) angstrom. It has a cell volume of 358.82(5) angstrom3 with Z = 1. The strongest six li nes of the X-ray powder diffraction pattern are [d in angstrom (I) (hk l)] 2.823, 2.813(100) (110,008); 5.63(85) (004); 2.251(33) (116, 0.0.1 0); 2.988(27) (105); 3.750(15) (006); 1.994(11) (200,118). Averaged el ectron microprobe analyses give the empirical formula Pb6.34Mo0.89squa re0.77O8.02Cl1.98 on the basis of 10 atoms [O + Cl]. The name is for R eginald F. D. Parkinson, mineral collector of Somerset, UK, who first found the mineral.