A Supposed Sövite from Oldoinyo Lengai, Tanzania: Result of Extreme Alteration of Alkali Carbonatite Lava

J. B. Dawson
Department of Geology and Geophysics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, U.K.

Abstract: A calcite-rich block in nephelinitic agglomerate at Oldoinyo Lengai comprises Sr-calcite, apatite, fluorite, a Ba-Mn oxide akin to romanéchite, and a distinctive Mn-Fe spinel. Formerly reported as sövite, on textural, mineralogical and stable isotope grounds it is now re-interpreted as a highly-altered natrocarbonatite lava. An implication of this study is that natrocarbonatite is not just a modern phenomenon, but has been extruded from Oldoinyo Lengai for at least around 1250 years.

Keywords: sövite • altered natrocarbonatite • Oldoinyo Lengai • Tanzania

Mineralogical Magazine; March 1993 v. 57; no. 386; p. 93-101; DOI: 10.1180/minmag.1993.057.386.09
© 1993, The Mineralogical Society
Mineralogical Society (www.minersoc.org)