Parisite-(La), ideally CaLa2(CO3)3F2, a new mineral from Novo Horizonte, Bahia, Brazil

• Published in: Mineralogical magazine Vol. 82; no. 1; pp. 133 - 144
• Main Authors: Menezes Filho, Luiz A. D, Chaves, Mario L. S. C, Chukanov, Nikita V, Atencio, Daniel, Scholz, Ricardo, Pekov, Igor, da Costa, Geraldo Magela, Morrison, Shaunna M, Andrade, Marcelo B, Freitas, Erico T. F, Downs, Robert T, Belakovskiy, Dmitriy I
• Format: Journal Article
• Language: English
• Published: London Mineralogical Society 01.02.2018; Cambridge University Press
• Subjects: almeidaite; Bahia Brazil; bastnaesite; Brazil; brockite; carbonates; chemical composition; coexisting minerals; crystal form; crystal structure; Crystals; fluocerite; fluorides; formula; halides; hematite; lanthanum; lattice parameters; metaigneous rocks; metals; metamorphic rocks; metarhyolite; Mineralogy; Minerals; monazite; Mula Mine; new minerals; nonsilicates; Novo Horizonte Brazil; optical properties; oxides; parisite; phosphates; physical properties; Quartz; rare earths; rhabdophane; Rio dos Remedios Group; rutile; single-crystal method; South America; space groups; Spectrum analysis; Tapera Brazil; unit cell; X-ray diffraction data; Brazil; Czech Republic; Paraguay; United States > US
• ISSN: 0026-461X; 1471-8022
• DOI: 10.1180/minmag.2017.081.028

Parisite-(La) (IMA2016-031), ideally CaLa2(CO3)3F2, occurs in a hydrothermal vein crosscutting a metarhyolite of the Rio dos Remedios Group, at the Mula mine, Tapera village, Novo Horizonte county, Bahia, Brazil, associated with hematite, rutile, almeidaite, fluocerite-(Ce), brockite, monazite-(La), rhabdophane-(La) and bastnasite-(La). Parisite-(La) occurs as residual nuclei (up to 5 mm) in steep doubly-terminated pseudo-hexagonal pyramidal crystals (up to 8.2 cm). Parisite-(La) is transparent, yellow-green to white, with a white streak and displays a vitreous (when yellow-green) to dull (when white) lustre. Cleavage is distinct on pseudo-{001}; fracture is laminated, conchoidal, or uneven. The Mohs hardness is 4 to 5, and it is brittle. Calculated density is 4.273 g cm-3. Parisite-(La) is pseudo-uniaxial (+), ω = 1.670(2) and ε = 1.782(5) (589 nm). The empirical formula normalized on the basis of 11 (O + F) atoms per formula unit (apfu) is Ca0.98(La0.83Nd0.51Ce0.37Pr0.16Sm0.04Y0.03)Σ1.94C3.03 O8.91 F2.09. The IR spectrum confirms the absence of OH groups. Single-crystal X-ray studies gave the following results: monoclinic (pseudo-trigonal), space group: C2, Cm, or C2/m, a = 12.356(1) Å, b = 7.1368(7) Å, c = 28.299(3) Å, β = 98.342(4)°, V = 2469.1(4) Å3 and Z = 12. Parisite-(La) is the La-dominant analogue of parisite-(Ce).