Tuzlaite, NaCa[B5O8(OH)2]·3H2O, a new mineral with a pentaborate sheet structure from the Tuzla salt mine, Bosnia and Hercegovina

• Published in: The American mineralogist 1994-06, Vol.79 (5-6), p.562-569
• Main Authors: Bermanec, Vladimir, Armbruster, Thomas, Tibljas, Darko, Sturman, Darko, Kniewald, Goran
• Format: Article
• Language: English
• Subjects: Bosnia; Bosnia-Herzegovina; chemically precipitated rocks; Condensed matter: structure, mechanical and thermal properties; crystal structure; Europe; evaporites; Exact sciences and technology; Inorganic compounds; Mineralogy; NaCa[B5O8(OH)2]·3H2O; nonsilicates; optical properties; pentaborates; Physics; salt; Salts; sedimentary rocks; Southern Europe; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Tuzla Mine; tuzlaite; X-ray absorption spectroscopy: exafs, nexafs, xanes, etc; X-ray data; X-ray diffraction and scattering; Yugoslavia
• ISSN: 0003-004X; 1945-3027

Tuzlaite, NaCa[B5O8(OH)2]3H2O, is a monoclinic sheet borate [P21/c, a 6.506(1), b 13.280(3), c 11.462(3) Å, β 92.97(2)°, Z = 4], occurring in nearly monomineralic veinlets formed in the course of dolomitic marl diagenesis at the Tuzla salt mine, in the NE part of Bosnia and Hercegovina. Intergrowths with halite have been observed where halite covers tuzlaite in later stages of diagenesis. Indexed XRD powder data are tabulated; strongest lines 8.638(100), 6.617(30), 2.868(29), 4.179(17), 2.586(15) Å. The crystal structure, including H positions, was solved and refined from X-ray single-crystal data to R = 2.8, Rw = 3.3%. Tuzlaite possesses a new type of pentaborate sheet structure with fourfold and threefold-coordinated B (5:2 Δ + 3T); borate triangles and tetrahedra form ten-membered rings. The sheets are connected by Na and Ca, which are coordinated to additional H2O. The new mineral is colourless to white. It is biaxial positive, with α 1.532, β 1.544, Γ 1.561(2). The optical orientation is β = b, Γ:a = 14° (in acute angle β). Tuzlaite has one perfect cleavage, parallel to 001, and H. 2-3; D 2.21, Dcalc 2.23 g/cm3. Tuzlaite is chemically related to the pentaborates probertite, NaCa B5O7(OH)43H2O, and ulexite, NaCaB5O6(OH)65H2O. The new mineral is named after the town of Tuzla, where it was found.