gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1986.050.358.12 Johninnesite, a New Sodium Manganese Arsenosilicate from the Kombat Mine, Namibia Dunn Pete J. Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20560, USA Peacor Donald R. Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Su Shu-Chun * Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA Nelen Joseph A. Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20560, USA von Knorring Oleg 21 Churchwood Avenue, Leeds LS16 5LF, England

Permanent address: Institute of Geology, Chinese Academy of Sciences, Beijing, People's Republic of China.

 12 1986 50 358 667 670 4 2 1986 Copyright © 1986, The Mineralogical Society 1986 Abstract

Johninnesite, ideally Na2Mg4Mn12As25+Si12O43(OH)6, is triclinic, P1 or P1¯, with a = 10.44(2), b = 11.064(6), c = 9.62(1) Å, α = 107.43(7), β = 82.7(1), γ = 111.6(1)°, V = 894(2) Å3, and Z = 1. It occurs as yellow-brown fibrous aggregates, associated with rhodonite, kentrolite, and richterite, from the Kombat Mine in Namibia. Johninnesite has cleavages on {100} and {010}, density of 3.48 (meas.), 3.51 (calc.) g/cm3. It is biaxial negative, with 2Vx = 41.9°, α = 1.6742(4), β = 1.6968(3), γ = 1.6999(3); dispersion r > υ, distinct.

 Keywords johninnesite new mineral Kombat Mine Namibia