FRANKHAWTHORNEITE, Cu2Te6+O4(OH)2, A NEW MINERAL SPECIES FROM THE CENTENNIAL EUREKA MINE, TINTIC DISTRICT, JUAB COUNTY, UTAH*

ANDREW C. ROBERTS
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8

JOEL D. GRICE
Mineral Sciences Section, Canadian Museum of Nature, Ottawa, Ontario K1P 6P4

ALAN J. CRIDDLE
Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K.

MARTIN C. JENSEN**
Mackay School of Mines, MS168, University of Nevada, Reno, Nevada 89557-0047, U.S.A.

DONALD C. HARRIS
Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8

ELIZABETH A. MOFFATT
Canadian Conservation Institute, 1030 Innes Road, Ottawa, Ontario K1A 0C8

* Geological Survey of Canada contribution number 34294.
** Present address: 121-2855 Idlewild Drive, Reno, Nevada 89509, U.S.A.


Abstract

Frankhawthorneite, ideally Cu2Te6+O4(OH)2, is monoclinic, P21/n (14), with unit-cell parameters refined from powder data: a 9.095(3), b 5.206(2), c 4.604(1) Å, 98.69(2) , V 215.5(1) Å3, a:b:c 1.7470:1:0.8844, Z = 2. The strongest eight lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 4.506(40)(110, 200), 4.337(60)(01), 3.838(50)(101), 2.891(70)(11), 2.598(100)(020,310,211), 1.834(40)(12), 1.713(40)(022) and 1.500(40)(330,231,600). The mineral is found on the dumps of the Centennial Eureka mine, Juab County, Utah, where it occurs as isolated crystals 0.1 mm in size or as groupings of crystals on drusy white quartz. Associated minerals include mcalpineite, pyrite, hematite, acanthite, chrysocolla, connellite, enargite, hinsdalite, svanbergite and an undefined Cu<0150>Zn<0150>Te-bearing pale green botryoidal crust. Individual crystals of frankhawthorneite are prismatic to stubby bladed, are subhedral to euhedral, and have slightly curved faces. They are elongate [001], with a length-to-width ratio of approximately 3:1. Forms are {010} major, and possible {100} and {011} minor. The mineral is transparent, medium leaf green, with a less intense streak of the same color and an uneven fracture. Frankhawthorneite is vitreous, brittle and nonfluorescent; H(Mohs) 3-4; D(calc.) 5.43 for the idealized formula, 5.44 g/cm3 for the empirical formula. In polished section, frankhawthorneite is weakly bireflectant and nonpleochroic. In reflected plane-polarized light in air it is pale grey, in oil it is purple-grey, with ubiquitous viridian green internal reflections. The anisotropy is weak with brown rotation tints. Measured reflectance values, in air and in oil, are tabulated. Electron- microprobe analyses yielded CuO 45.20, TeO3 48.77, H2O (calc.) [5.05], total [99.02] wt.%. The empirical formula, derived from crystal-structure analysis and electron-microprobe analyses, is Cu2.03Te99O4.00(OH)2.00, based on O = 6 and with (OH) = 2.00. The mineral name honors Professor Frank C. Hawthorne, University of Manitoba, for his many important contributions to the fields of mineralogy and crystallography, and especially for his ongoing studies of the crystal chemistry of Cu2+ oxysalt minerals.


Keywords: frankhawthorneite, new mineral species, copper hydroxide-tellurate, X-ray data, electron-microprobe data, reflectance data, Centennial Eureka mine, Juab County, Utah.