Abstract

Carlinite, Tl2S, occurs as small subhedral to anhedral grains with fine-grained quartz and hydrocarbon compounds in carbonaceous limestones exposed in the east pit of the Carlin mine, Nevada. Fresh carlinite is dark gray with a bright metallic luster and a dark gray to black streak. Carlinite rapidly oxidizes in air, causing exposed surfaces to become dull and darker in color. The crystallographic parameters of carlinite are: rhombohedral, space group R3, a = 12.12 ± 0.01 Å, c = 18.175 ± 0.005 Å, Z = 27, cell volume = 2310.5 ± 0.6 Å3. Carlinite displays perfect (0001) cleavage, an imperfect prismatic cleavage, and hackly fracture. The strongest X-ray diffraction peaks and relative intensities are: 3.030 Å, 1000; 2.290 Å, 33; l.749 Å, 30; 2.020 Å, 28. Powdered carlinite tends to show extreme preferred orientation because of the perfect basal cleavage. Vickers hardness is 23.5 ± 2.0 kg/mm2; Mohs hardness, 1; density, 8.1 ± 0.2 g/cm3 (meas), 8.55 g/cm3 (calc). In reflected light, carlinite is “galena white” with a faint bluish cast, weakly bireflectant, and moderately anisotropic, with polarization colors that range from brownish-gray to bluish-gray. Reflectances in air are: R650nm = 40.5-42.0; R589nm = 39.2 - 40.6; R546nm = 38.8 - 40.1 and R470nm = 39.6 - 41.3. Carlinite is essentially pure Tl2S; microprobe analysis yielded Tl = 92.93 and S = 7.17, in wt percent. The most abundant trace element, by emission spectrographic analysis, is As at levels less than 100 ppm. The new mineral is named after the Carlin gold deposit in which it was discovered.

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