Staringite, a new Sn–Ta mineral from north-eastern Brazil

Abstract

Summary Staringite, (Fe,Mn) 0·5 (Sn,Ti) 4·5 (Ta,Nb) 1·0 O 12 , occurs as inclusions in tapiolite from pegmatites at Seridózinho and Pedra Lavreda, Paraiba State, NE. Brazil. An indexed powder pattern is presented. The mineral is tetragonal with a 4·742 Å and c 9·535 Å, and most probably has a ‘trirutile’ structure. Electron-microprobe analysis yielded Ta 2 O 5 21·5%, Nb 2 O 5 1·8, SnO 2 73·3, TiO 2 0·03, FeO 3·7, MnO 0·3, sum 100·6%. D calc 7·17. Micro-indentation hardness (load 100 g) 1033–1187 kg/mm 2 ; reflectivity at 470 nm (R 0 ) 12·8 to (R′ e ) 14·5%, at 546 nm 12·1–13·9, at 589 nm 12·0–13·7, and at 650 nm 11·8–13·6; staringite is uniaxial positive.