On the occurrence of niobium-tantalum and other rare-element minerals in the Meldon aplite, Devonshire

Abstract

A number of rare-element minerals from the Meldon aplite are described, e.g. native arsenic and antimony, arsenolite, stibiconite, and various niobium-tantalum minerals. Some of the minerals are new to the occurrence and some may be new to the British Isles. Particular attention has been paid to the Nb-Ta minerals and a large number of electron-microprobe analyses for manganocolumbite, manganotantalite, and microlite are presented. Examination of numerous, minute crystals and fragments of columbite-tantalite revealed a complex oscillatory zoning, indicating a slow rate of cooling and perhaps incomplete miscibility of the isomorphous columbite-tantalite series.