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

Parisite-(La) (IMA2016-031), ideally CaLa₂(CO₃)₃F₂, 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_0.83Nd_0.51Ce_0.37Pr_0.16Sm_0.04Y_0.03)_Σ1.94C_3.03O_8.91F_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: 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) ų and Z = 12. Parisite-(La) is the La-dominant analogue of parisite-(Ce).