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Parkinsonite, (Pb,Mo, □)8O8Cl2, a new mineral from Merehead Quarry, Somerset

Published online by Cambridge University Press:  05 July 2018

R. F. Symes ,
G. Cressey ,
A. J. Griddle ,
C. J. Stanley ,
J. G. Francis  and
G. C. Jones
R. F. Symes
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
G. Cressey
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
A. J. Griddle
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
C. J. Stanley
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
J. G. Francis
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
G. C. Jones
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
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Abstract

Parkinsonite, ideally (Pb,Mo,□)8O8Cl2, is a new mineral from the Merehead Quarry, Cranmore, Somerset, England. It occurs as compact clusters 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 crystals were not found; intergrown crystalline aggregates are the usual form of occurrence. The maximum grain size is about 300 × 100 µm, but most grains are appreciably smaller. Parkinsonite was synthesized using high purity chemicals. The measured density of the synthetic material 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 sample. Parkinsonite is translucent. Reflectance spectra were obtained in air and in oil. Refractive indices calculated from these (at 589 nm) are for Ro, 2.58, and Re', 2.42, i.e. uniaxial negative. VHN50 is 113–133 from which the calculated Mobs hardness is 2–2.5.

X-ray studies show that parkinsonite is tetragonal with space group I4/mmm, I4̄2m, I4̄m2, I4/mm, or I422 and a 3.9922(3), c 22.514(2) Å. It has a cell volume of 358.82(5) Å3 with Z = 1. The strongest six lines of the X-ray powder diffraction pattern are [d in Å (I) (hkl)] 2.823, 2.813(100) (110,008); 5.63(85) (004); 2.251(33) (116, 0.0.10); 2.988(27) (105); 3.750(15) (006); 1.994(11) (200,118). Averaged electron microprobe analyses give the empirical formula Pb6.34Mo0.89□0.77O8.02Cl1.98 on the basis of 10 atoms [O + Cl]. The name is for Reginald F. D. Parkinson, mineral collector of Somerset, UK, who first found the mineral.

Keywords

parkinsonitenew minerallead molybdenum oxychlorideMerehead Quarry
Type
Mineralogy
Information
Mineralogical Magazine , Volume 58 , Issue 390 , March 1994 , pp. 59 - 68
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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