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A new mineral, chrisstanleyite, Ag2Pd3Se4, from Hope's Nose, Torquay, Devon, England

Published online by Cambridge University Press:  05 July 2018

W. H. Paar ,
A. C. Roberts ,
A. J. Criddle  and
D. Topa
W. H. Paar
Affiliation:
Institut für Mineralogie der Universitat, Hellbrunnerstr. 34. A-5020 Salzburg, Austria
A. C. Roberts
Affiliation:
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A OE8, Canada
A. J. Criddle
Affiliation:
Department of Mineralogy, The Natural History Museum, London SW7 KBD, UK
D. Topa
Affiliation:
Institut für Mineralogie der Universitat, Hellbrunnerstr. 34. A-5020 Salzburg, Austria
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Abstract

Chrisstanleyite, Ag2Pd3Se4, is a new mineral from gold-bearing carbonate veins in Middle Devonian limestones at Hope's Nose, Torquay, Devon, England. It is associated with palladian and argentian gold, fischesserite, clausthalite, eucairite, tiemannite, umangite, a Pd arsenide-antimonide (possibly mertieite II), cerussite, calcite and bromian chlorargyrite. Also present in the assemblage is a phase similar to oosterboschite, and two unknown minerals with the compositions, PdSe2 and HgPd2Se3. Chrisstanleyite occurs as composite grains of anhedral crystals ranging from a few µm to several hundred µm in size. It is opaque, has a metallic lustre and a black streak, VHN100 ranges from 371–421, mean 395 kp/mm2 (15 indentations), roughly approximating to a Mohs hardness of 5. Dcalc = 8.308 g/cm3 for the ideal formula with Z = 2. In plane-polarised reflected light, the mineral is very slightly pleochroic from very light buff to slightly grey-green buff; is weakly bireflectant and has no internal reflections. Bireflectance is weak to moderate (higher in oil). Anisotropy is moderate and rotation tints vary from rose-brown to grey-green to pale bluish grey to dark steel-blue. Polysynthetic twinning is characteristic of the mineral. Reflectance spectra and colour values are tabulated. Very little variation was noted in eleven electron-microprobe analyses on five grains, the mean is: Ag 25.3, Cu 0.17, Pd 37.5, Se 36.4, total 99.37 wt.%. The empirical formula (on the basis of ∑M + Se = 9) is (Ag2.01Cu0.02)∑2.03 Pd3.02Se3.95, ideally Ag2Pd3Se4. Chrisstanleyite is monoclinic, a 6.350(6), b 10.387(4), c 5.683(3) Å β 114.90(5)°, space group P21/m (11) or P21(4). The five strongest X-ray powder-diffraction lines [d in Å (I)(hkl)] are: 2.742 (100) (–121), 2.688 (80) (–221), 2.367 (50) (140), 1.956 (100) (–321,150) and 1.829 (30) (–321, 042). The name is in honour of Dr Chris J. Stanley of The Natural History Museum in London. The mineral and its name have been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association.

Keywords

chrisstanleyitenew mineralpalladium-silver selenidegoldselenide mineralsX-ray dataelectron-microprobe datareflectance dataHope's NoseDevonEngland
Type
Research Article
Information
Mineralogical Magazine , Volume 62 , Issue 2 , April 1998 , pp. 257 - 264
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

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