Reconsideration of ‘Soda-Minettes’

Sharon W. Bachinski*
Department of Geology, University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada
*The editors regret to report the death of Sharon Bachinski on 14 March 1986.

Abstract: It is shown here that dyke rocks of type localities for ‘soda-minettes’ are not minettes (= lamprophyres dominated by phlogopite and K-rich feldspar). It has long been suggested that ‘soda-minette’ also be applied to otherwise normal minettes from elsewhere that carry modally variable amounts of groundmass aegirine and/or, more commonly, arfvedsonitic to riebeckitic amphibole. Despite the presence of sodic pyriboles, these rocks are poorer in Na2O then minettes lacking these phases. ‘Soda-minette’ is thus misleading and self-contradictory to the many petrologists to whom ‘soda-’ legitimately connotes that the rock in question either has K/Na < 1 and/or is rich in albitic feldspar. To eliminate this ambiguity it is recommended, with the approval of twenty-six other petrologists, that ‘soda-minette’ no longer be used as a rock name. As minettes with Na-pyribole(s) are markedly K-rich and most are both ultrapotassic and peralkaline, independent of the modal abundance of the Na-pyrobile, it is suggested that one of these three chemical characteristics be utilized adjectivally in naming these minettes.

Keywords: minette • soda-minette • lamprophyre

Mineralogical Magazine; June 1986 v. 50; no. 356; p. 199-204; DOI: 10.1180/minmag.1986.050.356.02
© 1986, The Mineralogical Society
Mineralogical Society (