Clearcreekite, a new polymorph of Hg-3(1+)(CO3)(OH)center dot 2H(2)O, fromthe Clear Creek claim, San Benito County, California

Clearcreekite is a newly recognized polymorph of Hg-3(1+)(CO3)(OH). 2H(2)O (along with the previously described peterbaylissite). The mineral is monoc linic, space group P2(1)/c (14), with unit-cell parameters refined from pow der data: a 6.760(4), b 9.580(4), c 10.931(4) Angstrom, beta 105.53(5)degre es, V682.1(6) Angstrom (3), a:b:c = 0.7056:1:1.1410, Z = 4. The strongest s ix reflections in the X-ray powder-diffraction pattern [d in Angstrom (I)(h kl)] are: 7.09(70)(011), 5.32(40)((1) over bar 11), 4.62(90)(012), 2.831(10 0)(023), 2.767(100) (211,(2) over bar 21), and 2.391(40)(040,(2) over bar 0 4). The mineral is an extremely rare constituent in a small prospect pit ne ar the long-abandoned Clear Creek mercury mine, New Idria district, San Ben ito County, California. The mineral is found as an isolated cluster of crys tals in a shallow depression, associated with cinnabar and edoylerite, on a single specimen of brecciated silica-carbonate rock. Individual crystals d o not exceed 0.17 mm, in longest dimension and are subhedral, tabular, with major {001} and minor {010} forms. The mineral is transparent with a pale greenish yellow color and streak. Physical properties include: vitreous lus ter, uneven fracture, brittle, nonfluorescent, soft (grains punctured by an electron beam), calculated density 6.96 g/cm(3) (idealized formula). The m ineral becomes dark brown-black and opaque when subjected to X-radiation, a nd the change is irreversible. Electron-microprobe analysis yielded 84.65 w t.% Hg2O. The empirical formula, derived from results of a crystal-structur e analysis and of an electron-microprobe analysis, is Hg-2.92(1+)(C1.01O2.9 8)(OH)(1.04). 2H(2)O, based on O = 6. The idealized formula requires Hg2O 8 7.54, CO2 6.16, H2O 6.30, total 100.00 wt.%. The infrared-absorption spectr um confirms the presence of both CO3 and H2O. The mineral is named after th e type locality.