Bluebellite and mojaveite, two new minerals from the central Mojave Desert, California, USA

摘要

Bluebellite, Cu-6[I5+O3(OH)(3)](OH)(7)Cl and mojaveite, Cu-6[Te6+O4(OH)(2)](OH)(7)Cl, are new secondary copper minerals from the Mojave Desert. The type locality for bluebellite is the D shaft, Blue Bell claims, near Baker, San Bernardino County, California, while cotype localities for mojaveite are the E pit at Blue Bell claims and also the Bird Nest drift, Otto Mountain, also near Baker. The two minerals are very similar in their properties. Bluebellite is associated particularly with murdochite, but also with calcite, fluorite, hemimorphite and rarely dioptase in a highly siliceous hornfels. It forms bright bluish-green plates or flakes up to similar to 20 mu m x 20 mu m x 5 mu m in size that are usually curved. The streak is pale bluish green and the lustre is adamantine, but often appears dull because of surface roughness. It is non-fluorescent. Bluebellite is very soft (Mohs hardness similar to 1), sectile, has perfect cleavage on {001} and an irregular fracture. The calculated density based on the empirical formula is 4.746 g cm(-3). Bluebellite is uniaxial (-), with mean refractive index estimated as 1.96 from the Gladstone-Dale relationship. It is pleochroic O (bluish green) E (nearly colourless). Electron microprobe analyses gave the empirical formula Cu5.82I0.99Al0.02Si0.12O3.11(OH)(9.80)Cl-1.09 based on 14 (O+Cl) a.p.f.u. The Raman spectrum shows strong iodate-related bands at 680, 611 and 254 cm(-1). Bluebellite is trigonal, space group R3, with the unit-cell parameters: a = 8.3017(5), c = 13.259(1) angstrom, V = 791.4(1) angstrom(3) and Z = 3. The eight strongest lines in the powder X-ray diffraction (XRD) pattern are [d(obs)/angstrom (I) (hkl)]: 4.427(99)(003), 2.664(35)(211), 2.516(100)(21 (2) over bar), 2.213(9)(006), 2.103(29)(033,214), 1.899(47)(312,21 (5) over bar), 1.566(48)(140,217) and 1.479(29)(045,14 (3) over bar ,324).