PETERBAYLISSITE, HG-3(1-DOT-2H(2)O, A NEW MINERAL SPECIES FROM THE CLEAR-CREEK CLAIM, SAN-BENITO COUNTY, CALIFORNIA()(CO3)(OH)CENTER)

Peterbaylissite, idealized as Hg-3(1+)(CO3)(OH). 2H(2)O, is orthorhomb ic, space group Pcab (61), with unit-cell parameters refined from powd er data: a 11.130(2), b 11.139(3), c 10.725(3) Angstrom, V 1330(1) Ang strom(3), a:b:c = 0.9992:1:0.9628, Z = 8. The strongest six reflection s in the X-ray powder pattern [d in Angstrom(I)(hkl)] are: 4.84(50)(01 2), 2.969(70)(231), 2.786(70)(040,400), 2.648(100)(223), 2.419(60)(241 ,024,412), and 1.580(50)(623). The mineral is an extremely rare consti tuent in a small prospect pit near the long-abandoned Clear Creek merc ury mine, New Idria district, San Benito County, California. The miner al is most closely associated with ferroan magnesiochromite and is fou nd as isolated and clustered grains on a crust composed of ferroan mag nesite and quartz. Other mercury-bearing phases found on the holotype specimen include cinnabar, metacinnabar and native mercury. Individual crystals of peterbaylissite range in size from 20 mu m up to 0.2 mm, but the average length of crystals is approximately 0.1 mm. Crystals a re subhedral to euhedral, elongate [001], and possess a wedge-like sha pe with a conchoidal outline. Platy crystals also are present but are rare. The mineral is opaque, black to very dark red-brown color, with a dark brown-black streak. Physical properties include: submetallic to adamantine luster, irregular fracture, brittle, nonfluorescent, hardn ess less than 5, calculated density 7.14 g/cm(3) (for both the empiric al and idealized formulae). In polished section, peterbaylissite is we akly to moderately bireflectant and is nonpleochroic. In reflected pla ne-polarized light, it is grey with a slight blue tinge and possesses abundant orange and brilliant yellow-white internal reflections. The a nisotropy is weak, with dull and dark grey and brown rotation tints. M easured values of reflectance for two grains, in air and in oil, are t abulated. Electron-microprobe analyses yielded Hg2O 87.4(1.5) wt.%. Th e empirical formula, derived from crystal-structure analysis and elect ron-microprobe analyses, is Hg-3.00(1+)(CO3)(OH). 2H(2)O, based on O = 6. The idealized formula requires Hg2O 87.54, CO2 6.16, H2O 6.30, tot al 100.00 wt.%. Important features of the crystal structure are summar ized. This is the first natural occurrence of Hg1+ as an isolated ion in an oxysalt. The mineral is named for Professor Emeritus Peter Bayli ss, University of Calgary, for his many important contributions to str uctural and experimental mineralogy, and for his long-standing service to the International Centre for Diffraction Data.