gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1986.050.358.18 The Chemistry and Structure of Redledgeite Gatehouse B. M. 1 Jones G. C. 3 Pring A. 2 Symes R. F. 3 Department of Chemistry, Monash University, Clayton, Vic. 3168, Australia South Australian Museum, North Terrace, Adelaide, SA 5000, Australia Department of Mineralogy, British Museum (Natural History), Cromwell Road, London, SW7 5BD, England 12 1986 50 358 709 715 11 10 1985 25 6 1986 Copyright © 1986, The Mineralogical Society 1986 Abstract

Two distinct habits of redledgeite are described: small black bipyramidal crystals and yellow-green fibres. The mineral is a Ba-Cr-Ti oxide rather than a Mg-Cr-Ti oxide as previously supposed. Electron microprobe analysis gave Ba1.10(Cr1.82Ti5.95 Fe0.10V0.08)Σ7.95O16 and Ba1.27(Cr2.48Ti5.49Fe0.02)Σ7.99 O16 for the black and yellow-green forms respectively. The mineral is a monoclinic hollandite-type phase, space group I2/m, with a = 10.129(2); b = 2.959(1); c = 10.135(2) Å; β = 90.05(11)° and Z = 1; calculated density for the black form is 4.413 g cm−3. The crystal structure was refined to R 6.3%, Rw 7.4% using 1017 reflections with F > 3σ(F) from a set of 1062 unique reflections. Electron diffraction studies revealed weak superlattice reflections, with a period of 2.24b due to tunnel cation ordering.

 Keywords redledgeite crystal chemistry hollandite-type structure Red Ledge gold mine California