Eckhardite, (Ca,Pb)Cu2+Te6+O5(H2O), is a new tellurate mineral from Otto Mountain near Baker, California, U.S.A. It occurs in vugs in quartz in association with Br-rich chlorargyrite, gold, housleyite, khinite, markcooperite, and ottoite. It is interpreted as having formed from the partial oxidation of primary sulfides and tellurides during or following brecciation of quartz veins. Eckhardite is monoclinic, space group P21/n, with unit-cell dimensions a = 8.1606(8), b = 5.3076(6), c = 11.4412(15) Å, β = 101.549(7)°, V = 485.52(10) Å3, and Z = 4. It forms as needles or blades up to about 150 × 15 × 5 μm in size, typically in radial or sub-radial aggregates, but also as isolated needles. The color is light bluish green and the streak is very pale bluish green. Crystals are transparent with vitreous to subadamantine luster. The Mohs hardness is estimated at between 2 and 3. Eckhardite is brittle with an irregular fracture and one likely (but not observed) cleavage on {101}. The calculated density based on the empirical formula is 4.644 g/cm3. The mineral is biaxial (−), with indices of refraction of α = 1. 770 (calc), β = 1.860 (calc), and γ = 1.895(5). The measured 2V is 61.2(5)°, dispersion is r < v, perceptible and the optical orientation is Z =
© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号 地址:北京市海淀区学院路29号 邮编:100083 电话:办公室:(+86 10)66554848;文献借阅、咨询服务、科技查新:66554700 |