Oxycalciomicrolite, (Ca,Na)2(Ta,Nb,Ti)2O6(O,F), a new member of the microlite group (pyrochlore supergroup) from the Paleoproterozoic São João del Rei Pegmatite Province, Minas Gerais state, Brazil

Victor Hugo Riboura Menezes da Silva, Ciro Alexandre Ávila, Reiner Neumann, Fabiano Richard Leite Faulstich, Felipe Emerson André Alves, Filipe Barra de Almeida, Tais Proença Cidade, Sarah Siqueira da Cruz Guimarães Sousa
2020 Mineralogical magazine  
Oxycalciomicrolite [(Ca,Na) 2 (Ta,Nb,Ti) 2 O 6 (O,F)] is a new member of microlite group mineral found in the saprolite of the weathered Fumal pegmatite, located close to the city of Nazareno, Minas Gerais state, Brazil. It occurs as an accessory mineral associated with quartz, albite, microcline, muscovite, columbite subgroup minerals, cassiterite, hematite, ilmenite, monazite-(Ce), xenotime-(Y), zircon, beryl, spinel, epidote and garnet group minerals. Oxycalciomicrolite is found forming
more » ... found forming octahedral crystals, occasionally modified to rhombododecahedra, ranging from 0.2 to 0.5 mm in size. The crystals are brownish-yellow to brownish-red and translucent, with white streak and vitreous to resinous lustre. The tenacity is brittle, with a Mohs hardness of 5 -5½. Cleavage and parting are not observed, being the fracture conchoidal. Different analytical techniques as electron microprobe, Raman and infrared spectroscopies and X-ray powder diffraction were applied to characterize this mineral. The oxycalciomicrolite is isotropic, n calc. = 2.037, and the calculated density is 6.333 g/cm 3 . The composition is analysed by electron microprobe using wavelength dispersive spectrometry (WDS). The unit-cell parameters obtained by Pawley fitting from powder X-ray diffraction data are a = 10.4325(4) Å, V = 1135.46(14) ų, Z = 8. The name of this new mineral was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA-CNMNC) registration IMA 2019-110.
doi:10.1180/mgm.2020.74 fatcat:6qqcjs7f2je65kmnuufkpcq6r4