ERNIENICKELITE, NIMN3O7-CENTER-DOT-3H2O, A NEW MINERAL SPECIES FROM THE SIBERIA COMPLEX, WESTERN-AUSTRALIA - COMMENTS ON THE CRYSTALLOGRAPHY OF THE CHALCOPHANITE GROUP

Ernienickelite is a new mineral species in the chalcophanite g-up from the SM7 pit, Siberia ultramafic complex, Western Australia, Australia . It occurs in a Ni-Co laterite as a rare constituent in cavities of q uartz (chalcedony) associated with goethite, magnesite, a serpentine-g roup mineral, nimite and nontronite. It forms opaque, red-black plates to 0.5 mm in diameter and rosettes of plates up to 0.8 mm across. It is soft, H almost-equal-to 2, brittle with a splintery fracture, and c haracterized by a perfect {001} cleavage. D(calc) = 3.83 g/cm3 and D(m eas.) = 3.84 g/cm3. Uniaxial negative, omega) > 2.00, epsilon = 1.97(2 ). It is trigonal, R3BAR or R3, a 7.514(2), c 20.52(2) angstrom and Z = 6. The strongest X-ray-diffraction lines in the powder pattern [d in angstrom (I)(hkl)] are: 6.84(10)(003), 4.01(2)(10(4)) 2.219(3)(214), 1.884(2)(217) and 1.575(2)(2,1,10). An analysis by electron microprobe gave: MnO2 68.25, NiO 16.68, CoO 0.30, MgO 0.30, H2O (according to st oichiometry of chalcophanite structure) 13.94, total 99.47 wt.%, which yields the empirical formula (Ni0.87Mg0.03Mn0.04Co0.02)SIGMA0.96Mn3O7 .3H2O, or simply, NiMn34+O7.3H2O. The crystal structures of ernienicke lite and chalcophanite are compared to those of lithiophorite and cian ciulliite. The X-ray powder-diffraction data for chalcophanite and aur orite are corrected, refined and indexed.