Johninnesite, a New Sodium Manganese Arsenosilicate from the Kombat Mine, Namibia

Pete J. Dunn, Donald R. Peacor, Shu-Chun Su^*, Joseph A. Nelen and Oleg von Knorring

Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20560, USA
Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA
Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA
Department of Mineral Sciences, Smithsonian Institution, Washington, DC 20560, USA
21 Churchwood Avenue, Leeds LS16 5LF, England

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

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 2V_x = 41.9°, α = 1.6742(4), β = 1.6968(3), γ = 1.6999(3); dispersion r > υ, distinct.

Mineralogical Magazine; December 1986 v. 50; no. 358; p. 667-670; DOI: 10.1180/minmag.1986.050.358.12
© 1986, The Mineralogical Society
Mineralogical Society (www.minersoc.org)