Weissbergite, TlSbS<2), a new mineral from the Carlin gold deposit, Nevada

Weissbergite, TlSbS₂, occurs as irregular, broken or fractured grains, 0.5 mm in maximum dimension, in silicified, brecciated, dolomitic carbonate rocks in the east pit of the Carlin gold deposit, Nevada. Weissbergite is opaque, steel-gray in thick plates, and bright metallic in luster on fresh surfaces. The mineral is triclinic and apparently lacks a center of symmetry. Approximate cell constants are a = 11.8, b = 6.4, c = 6.1A; α = 109.9°, β = 81.8°, and γ = 105.4°; Z = 4; cell volume = 420A³. Strongest X-ray diffraction lines and their relative intensities (subject to strong preferred orientation) are: 2.971 (100), 3.583 (9), 3.651 (9), and 2.839 (7), 40 lines were observed. Weissbergite displays several cleavages: one, perfect; two, excellent; and at least one, good. Its Vickers hardness is about 35 kg mm⁻² (Mohs hardness, about 1.5). The measured density of synthetic TlSbS₂ is 5.79(5) g cm⁻³; calculated density is 6.1 g cm ⁻³. In reflected light the mineral is creamy white, weakly bireflectant, and strongly anisotropic, with polarization colors of blue-green, blue-black, orange-brown, and gray. Reflectances (R) in air are: 650nm = 32.1–33.8; 589nm = 34.5–35.8; 546nm = 35.0–36.8; and 470nm = 36.0–38.4. Thin plates in transmitted light show pleochroism in deep colors, ranging from red to orange-red and yellow-orange. Weissbergite is essentially pure TlSbS₂; electron microprobe analyses gave T1 52.7, Sb 31.2, S 16.4, sum 100.3 weight percent. The most abundant trace elements, determined by emission spectrographic analysis, are 300 ppm As and 200 ppm Fe. The mineral is named in honor of Dr. Byron G. Weissberg, Chemistry Division, D.S.I.R., New Zealand.