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

ABSTRACT Parisite-(La) (IMA2016-031), ideally CaLa 2 (CO 3 ) 3 F 2 , occurs in a hydrothermal vein crosscutting a metarhyolite of the Rio dos Remédios 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 bastnäsite-(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 Ca 0.98 (La 0.83 Nd 0.51 Ce 0.37 Pr 0.16 Sm 0.04 Y 0.03 ) Σ1.94 C 3.03 O 8.91 F 2.09 . The IR spectrum confirms the absence of OH groups. Single-crystal X-ray studies gave the following results: monoclinic (pseudo-trigonal), space group: C 2, Cm, or C 2/ m, a = 12.356(1) Å, b = 7.1368(7) Å, c = 28.299(3) Å, β = 98.342(4)°, V = 2469.1(4) Å 3 and Z = 12. Parisite-(La) is the La-dominant analogue of parisite-(Ce).