Bortolanite, Ca2(Ca1.5Zr0.5)Na(NaCa)Ti(Si2O7)2(FO)F2, a new rinkite-group (seidozerite supergroup) TS-block mineral from the Bortolan Quarry, Pocos de Caldas Massif, Minas Gerais, Brazil

• Published in: Canadian mineralogist Vol. 60; no. 4; pp. 699 - 712
• Main Authors: Day, Maxwell C, Sokolova, Elena, Hawthorne, Frank C, Horvath, Laszlo, Pfenninger-Horvath, Elsa
• Format: Journal Article
• Language: English
• Published: Mineralogical Association of Canada 01-07-2022
• Subjects: aegirine; Bortolan Quarry; bortolanite; Brazil; chain silicates; chemical composition; clinopyroxene; coexisting minerals; crystal structure; formula; framework silicates; gotzenite; lattice parameters; Minas Gerais Brazil; Mineralogy; nepheline; nepheline group; new minerals; pectolite; Pocos de Caldas Massif; pyroxene group; refinement; rinkite group; seidozerite supergroup; silicates; South America; space groups; wollastonite group; X-ray diffraction data
• ISSN: 0008-4476; 1499-1276
• DOI: 10.3749/canmin.2200001

Bortolanite (IMA 2021-040a), ideally Ca2(Ca1.5Zr0.5) Na(NaCa) Ti(Si2O7)2(FO)F2, is a rinkite-group (seidozerite supergroup) TS-block mineral from Pocos de Caldas massif, Minas Gerais, Brazil. Associated minerals are gotzenite, nepheline, alkali feldspar, aegirine, natrolite, analcime, and manganoan pectolite. Bortolanite shows complex compositional zoning with gotzenite and is visually indistinguishable from gotzenite. Bortolanite is pale-yellow to brown and has a vitreous luster. Cleavage is perfect parallel to {100}. Mohs hardness is 5. Bortolanite fluoresces weak yellow under ultraviolet light (100-280 nm). Dcalc.=3.195 g/cm3. Bortolanite is biaxial (+) with refractive indices (λ=589.3 nm) α=1.673(2), β=1.677(2), γ=1.690(2); 2Vmeas.=56(2)°, 2Vcalc.=58.4°. Chemical analysis by electron microprobe gave Nb2O5 1.07, HfO2 0.20, ZrO2 6.70, TiO2 9.94, SiO2 32.49, Gd2O3 0.12, Nd2O3 0.37, Ce2O3 1.25, La2O3 0.65, Y2O3 0.31, FeO 0.59, MnO 1.46, CaO 31.15, Na2O 8.36, F 6.95, O=F -2.93, sum 98.68 wt.%. The empirical formula based on 18 (O+F) apfu is (Ca1.88La0.03Ce0.06Nd0.02Gd0.01)Σ2 [Ca1.56(Zr0.41Hf0.01Y0.02)Σ0.44]Σ2 (Na0.85Ca0.15)Σ1 (Na1.18Ca0.60Mn0.16Fe2+0.06)Σ2 (Ti0.94Nb0.06)Σ1 (Si4.07O14)(O1.24F0.76)Σ2F2, Z=1. The simplified formula is Ca2(Ca,Zr)2Na(Na,Ca)2Ti(Si2O7)2(O,F)2F2. Bortolanite is triclinic, space group P1̄, a 9.615(3), b 5.725(2), c 7.316(2) Å, α 89.91(1), β 101.14(1), γ 100.91(1)°, V 387.7(3) Å3. The crystal structure was refined to R1=3.19% on the basis of 2194 unique reflections [F>4σ(F)] measured using a Bruker APEX II ULTRA three-circle diffractometer with a rotating-anode generator (MoKα), multilayer optics, and an APEX II 4K CCD detector. The crystal structure of bortolanite is a framework of TS (Titanium-Silicate) blocks [structure type B3(RG)], where the TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block exhibits linkage and stereochemistry typical for the rinkite group where Ti(+Nb+Zr)=1 apfu. The O sheet is composed of Ti-dominant MO(1) octahedra, [8]Na-dominant MO(2) polyhedra and (Na,Ca) MO(3) octahedra. In the H sheet in bortolanite, Si2O7 groups link to (Ca1.5Zr0.5) MH and Ca-dominant AP octahedra. Along a, TS blocks link directly through common edges of MH and AP polyhedra and common vertices of MH, AP, and Si polyhedra of the H sheets belonging to two TS blocks. The name bortolanite is after the locality: the Bortolan quarry in the Pocos de Caldas massif, Brazil. Bortolanite is isostructural with three rinkite-group minerals: fogoite-(Y), hainite-(Y), and gotzenite.