Manganese Valency and the Colour of the Mn2AsO4(OH) Polymorphs Eveite and Sarkinite

Ulf Hålenius and Erika Westlund
Department of Mineralogy, Swedish Museum of Natural History, P.O. Box 50007, SE-10405 Stockholm, Sweden
Department of Geology and Geochemistry, Stockholm University, SE-10691 Stockholm, Sweden

Abstract: Polarized optical absorption spectra of single crystals of the two dimorphic Mn2AsO4(OH)-minerals eveite and sarkinite show that minor concentrations of Mn3+ at the octahedral site determine the colour and cause the distinct pleochroism in green and yellow of eveite. In the sarkinite spectra only absorption bands due to spin-forbidden d-d transitions in Mn2+ at six- and five-coordinated sites are observed, which produce a weak flesh-red mineral colour and a very faint pleochroism.

Keywords: eveite • sarkinite • optical spectroscopy • Långban • Sweden

Mineralogical Magazine; February 1998 v. 62; no. 1; p. 113-119; DOI: 10.1180/002646198547503
© 1998, The Mineralogical Society
Mineralogical Society (