TEDHADLEYITE, Hg2+Hg1+10O4I2(Cl,Br)2, A NEW MINERAL SPECIES FROM THE CLEAR CREEK CLAIM, SAN BENITO COUNTY, CALIFORNIA

Abstract

Tedhadleyite, a new mineral species of ideal composition Hg 2+ Hg 1+ 10 O 4 I 2 (Cl,Br) 2 , is triclinic, A 1, with unit-cell parameters refined from X-ray powder data: a 7.014(4), b 11.855(6), c 12.601(6) A, α 115.56(4), β 82.57(4), γ 100.57(4)°, V 927.7(8) A 3 , a:b:c 0.5916:1:1.0629, Z = 2. The strongest eight lines of the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 5.281(50)(020,111), 3.143(90)(131,222), 3.005(70)(122), 2.981(50)(211), 2.885(100)(113), 2.675(90)(124, 233, 131), 2.508(40)(213) and 1.624(35)(035). The mineral occurs on a single specimen collected from a small prospect pit near the long-abandoned Clear Creek mercury mine, New Idria district, San Benito County, California. It is most closely associated with native mercury, calomel and traces of cinnabar, eglestonite and montroydite in a host rock principally composed of quartz and magnesite. Tedhadleyite occurs in a quartz-lined vug as a somewhat elongate spheroidal anhedral mass, 0.3 mm in diameter, which is partly hollow. The mineral is very dark red to black with a red streak. Physical properties include: adamantine to submetallic luster, opaque to translucent (on thin edges), nonfluorescent, poor {010} cleavage, brittle, uneven fracture, hardness less than 3, calculated density 9.43 g/cm 3 (for the chemical formula and unit-cell parameters derived from the crystal structure). In polished section, tedhadleyite is very weakly bireflectant, nonpleochroic and moderately anisotropic in shades of grey. In reflected plane-polarized light, it is bluish white with ubiquitous deep red to purplish red internal reflections. Measured reflectance values obtained in air and in oil for a single fragment are tabulated. Averaged and corrected results of electron-microprobe analyses yielded HgO 8.36, Hg 2 O 80.50, I 11.11, Cl 2.20, Br 1.62, sum 103.79, less O = I + Cl + Br 1.36, total 102.43 wt.%, corresponding to Hg 1.0 2+ Hg 1+ 9.8 O 3.7 I 2.2 (Cl 1.6 Br 0.5 ) ∑2.1 , based on O + I + Cl + Br = 8 apfu (atoms per formula unit). The original value for Hg, 85.15 wt.%, was partitioned in a ratio of 1 HgO : 10 Hg 2 O after the crystal structure was determined. The mineral name honors Ted A.Hadley of Sunnyvale, California.