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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

Published online by Cambridge University Press:  25 September 2020

Victor H.R. Menezes da Silva Open the ORCID record for Victor H.R. Menezes da Silva [Opens in a new window] ,
Ciro A. Ávila ,
Reiner Neumann ,
Fabiano R.L. Faulstich ,
Felipe E.A. Alves ,
Filipe B. de Almeida ,
Tais Proença Cidade  and
Sarah Siqueira da Cruz Guimarães Sousa
Victor H.R. Menezes da Silva*
Affiliation:
Programa de Pós-Graduação em Geologia, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21949-900, Ilha do Fundão, Rio de Janeiro, RJ, Brazil
Ciro A. Ávila
Affiliation:
Programa de Pós-Graduação em Geologia, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21949-900, Ilha do Fundão, Rio de Janeiro, RJ, Brazil Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista s/n, 20940-040, São Cristóvão, Rio de Janeiro, RJ, Brazil
Reiner Neumann
Affiliation:
Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista s/n, 20940-040, São Cristóvão, Rio de Janeiro, RJ, Brazil CETEM – Centro de Tecnologia Mineral, Setor de Caracterização Tecnológica, Avenida Pedro Calmon, 900, 22941-908, Ilha do Fundão, Rio de Janeiro, RJ, Brazil
Fabiano R.L. Faulstich
Affiliation:
Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista s/n, 20940-040, São Cristóvão, Rio de Janeiro, RJ, Brazil
Felipe E.A. Alves
Affiliation:
Programa de Pós-Graduação em Geologia, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21949-900, Ilha do Fundão, Rio de Janeiro, RJ, Brazil
Filipe B. de Almeida
Affiliation:
Instituto de Química, Universidade Federal Fluminense, Rua Outeiro de São João Batista, s/n°, 24020-141, Campus do Valonguinho, Niterói, RJ, Brazil
Tais Proença Cidade
Affiliation:
CETEM – Centro de Tecnologia Mineral, Setor de Caracterização Tecnológica, Avenida Pedro Calmon, 900, 22941-908, Ilha do Fundão, Rio de Janeiro, RJ, Brazil
Sarah Siqueira da Cruz Guimarães Sousa
Affiliation:
Programa de Pós-Graduação em Geologia, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21949-900, Ilha do Fundão, Rio de Janeiro, RJ, Brazil Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista s/n, 20940-040, São Cristóvão, Rio de Janeiro, RJ, Brazil
*
*Author for correspondence: Victor H.R. Menezes da Silva, Email: [email protected]
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Abstract

Oxycalciomicrolite (IMA2019-110), (Ca,Na)2(Ta,Nb,Ti)2O6(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 as 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; the fracture is conchoidal. Electron microprobe analysis, Raman and infrared spectroscopies and X-ray powder diffraction were applied to characterise this mineral. Oxycalciomicrolite is isotropic, ncalc. = 2.037, and the calculated density is 6.333 g/cm3. The composition is (Ca1.57□0.26Na0.06Sn0.03Sr0.03U0.02Mn0.02Fe0.01Ce0.01)∑2.00(Ta1.79Nb0.18Ti0.03)∑2.00O6.00[O0.64F0.19□0.17]∑1.00 analysed by electron microprobe using wavelength dispersive spectrometry. The unit-cell parameters obtained by Pawley fitting from powder X-ray diffraction data are a = 10.4325(4) Å and V = 1135.46(14) Å3 with Z = 8.

Keywords

oxycalciomicrolitepyrochlore supergroupmicrolite groupFumal pegmatiteSão João del Rei Pegmatite Province
Type
Article
Information
Mineralogical Magazine , Volume 84 , Issue 6 , December 2020 , pp. 854 - 858
Copyright
Copyright © The Author(s), 2020. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland

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Footnotes

Associate Editor: Sergey V. Krivovichev

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