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

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.

MILOTAITE, PdSbSe, A NEW PALLADIUM MINERAL SPECIES FROM PREDBORICE, CZECH REPUBLIC

“…1b). It corresponds chemically to the Ag-dominant endmember of the series Ag 2 Pd 3 Se 4 -Cu 2 Pd 3 S 4 , described by Paar et al (1998) as a new mineral species from Hope's Nose, Devon, United Kingdom.…”

“…During a systematic study of polished sections prepared of material from Předbořice, two further platinumgroup minerals were observed: chrisstanleyite (Paar et al 1998) and yet another palladium-dominant phase, the newly recognized analogue of synthetic PdSbSe. The new Pd-Sb selenide is named after Milota Makovicky (b.…”

Verbeekite, monoclinic PdSe2, a new mineral from the Musonoi Cu-Co-Mn-U mine, near Kolwezi, Shaba Province, Democratic Republic of Congo

“…58828'N, long. 3828'W) (Paar et al, 1998 and references therein which describe the mineralization found at Hope's Nose). The mineral name honours Dr Théodore Verbeek (1927À1991) who was the first geoscientist to study the Musonoi Se-bearing lens mineralization (1955À1967) and who, along with Dr R. Oosterbosch, first documented (in internal mining reports) the existence of palladium selenides.…”

PALLADIUM AND PLATINUM MINERALS FROM THE SERRA PELADA Au-Pd-Pt DEPOSIT, CARAJAS MINERAL PROVINCE, NORTHERN BRAZIL

“…Note that micro-analytical data suggest the empirical formula (Pd,Hg,Pb) 3 Se, raising the question whether there is a compositional series between Se-and As-rich (atheneite) end-members. More importantly, however, a Pd-Hg-Se association is known from Au-Se-bearing hydrothermal veins (Mernagh et al 1994, Paar et al 1998, Nickel 2002, Stanley et al 2002, for which a temperature of formation of about 100°C has been proposed (Simon et al 1997).…”