Abstract The occurrence of five rare minerals in the Eastern Brazilian Pegmatite Province, northeastern Minas Gerais, is described and discussed: bergslagite [CaBe(AsO4)(OH)] from the Manoel Fonseca mine, Coronel Murta county; herderite [CaBe(PO4)F] from the Funil mine, Medina county; lithiophosphate [Li3PO4] from the Cachoeira mine, Araçuaí/Itinga counties; lithiotantite [Li(Ta,Nb)3O8] from the Murundu mine, Itinga county; and kosnarite [KZr2(PO4)3] from Mario Pinto mine, Itinga county. The host pegmatites of these minerals, with their respective main chemical and/or mineralogical features are also presented. As a consequence of such discoveries, Raman spectra for lithiotantite and lithiophosphate were made available, and crystal structure refinement for lithiotantite was performed.

Abstract Important spodumene-rich pegmatites have been mined by CBL (Companhia Brasileira de Lítio, Brazilian Lithium Co.) at the Cachoeira mine (northeastern Minas Gerais state) since the 1990's. In this deposit, black platy crystals resembling columbitetantalite are also found; they were analyzed by electronic microprobe as part of the first author's master's degree dissertation. The Cachoeira pegmatite group comprises several spodumene-rich bodies that consist of pertitic microcline, spodumene (on average 23vol%), albite, quartz and muscovite, totalizing more than 95% of the bodies' volume. Analyses on 27 samples of supposedly Nb-tantalates showed a high variation of Ta, Nb and Sn contents, which has been observed inclusive in individual crystals, causing color variation on backscattered electrons images. Surprisingly, analyses on some grains also revealed the presence of ixiolite, a mineral species that has never been described in that region; it is characterized by high SnO2 contents (up to ~16wt%). Columbite-(Fe) phase represents 42% of total Nb-tantalates analyzed samples, tantalite-( Fe) 19%, columbite-(Mn) 3% and ixiolite, 36%. Cassiterite, also observed, shows significant Ta2O5 contents, probably indicating general exsolution processes.