CLEARCREEKITE, A NEW POLYMORPH OF Hg1+3(CO3)(OH){middle dot}2H2O, FROM THE CLEAR CREEK CLAIM, SAN BENITO COUNTY, CALIFORNIA

Abstract

Clearcreekite is a newly recognized polymorph of Hg 1+ 3 (CO 3 )(OH)·2H 2 O (along with the previously described peterbaylissite). The mineral is monoclinic, space group P 2 1 / c (14), with unit-cell parameters refined from powder data: a 6.760(4), b 9.580(4), c 10.931(4) A, β 105.53(5)°, V 682.1(6) A 3 , a:b:c = 0.7056:1:1.1410, Z = 4. The strongest six reflections in the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 7.09(70)(011), 5.32(40)(111), 4.62(90)(012), 2.831(100)(023), 2.767(100) (211, 221), and 2.391(40)(040,204). The mineral is an extremely rare constituent in a small prospect pit near the long-abandoned Clear Creek mercury mine, New Idria district, San Benito County, California. The mineral is found as an isolated cluster of crystals in a shallow depression, associated with cinnabar and edoylerite, on a single specimen of brecciated silica–carbonate rock. Individual crystals do 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 luster, uneven fracture, brittle, nonfluorescent, soft (grains punctured by an electron beam), calculated density 6.96 g/cm 3 (idealized formula). The mineral becomes dark brown-black and opaque when subjected to X-radiation, and the change is irreversible. Electron-microprobe analysis yielded 84.65 wt.% Hg 2 O. The empirical formula, derived from results of a crystal-structure analysis and of an electron-microprobe analysis, is Hg 1+ 2.92 (C 1.01 O 2.98 )(OH) 1.04 ·2H 2 O, based on O = 6. The idealized formula requires Hg 2 O 87.54, CO 2 6.16, H 2 O 6.30, total 100.00 wt.%. The infrared-absorption spectrum confirms the presence of both CO 3 and H 2 O. The mineral is named after the type locality.