Bluebellite and mojaveite, two new minerals 

from the central Mojave Desert, California, USA

Stuart J. Mills¹, Anthony R. Kampf², Andrew G. Christy³, Robert M. Housley⁴, George R. Rossman⁴, Robert E. Reynolds⁵ and Joe Marty⁶

¹Geosciences, Museum Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia
²Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA
³Centre for Advanced Microscopy, Australian National University, Canberra, ACT 0200, Australia
⁴Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁵220 South Buena Vista Street, Redlands, CA 92373, USA
⁶5199 E. Silver Oak Road, Salt Lake City, UT 84108, USA

ABSTRACT

    Bluebellite, Cu₆[I⁵⁺O₃(OH)₃](OH)₇Cl, and mojaveite, Cu₆[Te⁶⁺O₄(OH)₂](OH)₇Cl, 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 Birds 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 about 20 × 20 × 5 µm 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 ≈ 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 Cu_5.82I_0.99Al_0.02Si_0.12O_3.11(OH)_9.80Cl_1.09 based on 14 (O+Cl) pfu. 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) Å, V = 791.4(1) ų and Z = 3. The eight strongest lines in the X-ray powder diffraction pattern are [d_obs/Å (I) (hkl)]: 4.427(99)(003), 2.664(35)(211), 2.516(100)(21-2), 2.213(9)(006), 2.103(29)(033,214), 1.899(47)(312,21-5), 1.566(48)(140,217) and 1.479(29)(045,14-3,324).

    Mojaveite occurs at the Blue Bell claims in direct association with cerussite, chlorargyrite, chrysocolla, hemimorphite, kettnerite, perite, quartz and wulfenite, while at the Bird Nest drift, it is associated with andradite, chrysocolla, cerussite, burckhardtite, galena, goethite, khinite, mcalpineite, thorneite, timroseite, paratimroseite, quartz and wulfenite. It has also been found at the Aga mine, Otto Mountain, with cerussite, chrysocolla, khinite, perite and quartz. Mojaveite occurs as irregular aggregates of greenish-blue plates flattened on {001} and often curved, which rarely show a hexagonal outline, and also occurs as compact balls, from sky blue to medium greenish blue in colour. Aggregates and balls are up to 0.5 mm in size. The streak of mojaveite is pale greenish blue, while the luster may be adamantine, pearly or dull, and it is non-fluorescent. The Mohs hardness is ≈ 1. It is sectile, with perfect cleavage on {001} and an irregular fracture. The calculated density is 4.886 g cm^-3, based on the empirical formulae and unit cell dimensions. Mojaveite is uniaxial (‒), with mean refractive index estimated as 1.95 from the Gladstone-Dale relationship. It is pleochroic O (greenish blue) >> E (light greenish blue). The empirical formula for mojaveite, based on 14 (O+Cl) pfu, is Cu_5.92Te_1.00Pb_0.08Bi_0.01O₄(OH)_8.94Cl_1.06. The most intense Raman bands occur at 694, 654 (poorly resolved), 624, 611 and 254 cm^-1. Mojaveite is trigonal, space group R3, with the unit cell parameters: a = 8.316(2), c = 13.202(6) Å and V = 790.7(1) ų. The eight strongest lines in the X-ray powder diffraction pattern are [d_obs/Å (I) (hkl)]: 4.403(91)(003), 2.672(28)(211), 2.512(100)(21-2), 2.110(27)(033,214), 1.889(34)(312,21-5,22-3), 1.570(39)(404,140,217), 1.481(34)(045,14-3,324) and 1.338(14)(422). Diffraction data could not be refined, but stoichiometries and unit cell parameters imply that bluebellite and mojaveite are very similar in crystal structure. Structure models that satisfy bond valence requirements are presented that are based on stackings of brucite-like Cu₆MX₁₄ layers, where M = (I or Te) and X = (O, OH and Cl). Bluebellite and mojaveite provide a rare instance of isotypy between an iodate containing I⁵⁺ with a stereoactive lone pair and a tellurate containing Te⁶⁺ with no lone pair.