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Jadarite, LiNaSiB₃O₇(OH), a new mineral species from the Jadar Basin, Serbia

¹ Department of Mineralogy, Natural History Museum, London SW7 5BD, UK
² Rio Tinto, Unit 34 Hither Green Ind. Est., Clevedon, North Somerset, BS21 6XU, UK
³ Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8, Canada
⁴ Materials Technology Laboratories, Natural Resources Canada, 568 Booth Street, Ottawa, Ontario, K1A 0G1, Canada
⁵ Institute for Chemical Process and Environmental Technology, National Research Council Canada, 1200 Montreal Road, Ottawa, Ontario, K1A 0R6, Canada
⁶ Canadian Museum of Nature, P.O. Box 3443, Station "D", Ottawa, Ontario, K1P 6P4, Canada

^* Corresponding author, e-mail: c.stanley{at}nhm.ac.uk

Jadarite, ideally LiNaSiB₃O₇(OH), is a new mineral species from the Jadar Basin, Serbia. It occurs as massive white aggregates, several metres thick, and is relatively free from inclusions and intergrowths; however, individual subhedral (tabular, elongate) to anhedral crystals rarely exceed 5–10 µm in size. It is associated with calcite, dolomite, K-feldspar, rutile, albite, ilmenite, pyrite, and fine-grained muscovite. Searlesite, analcime, chlorite, and quartz have also been identified. Jadarite is translucent (opaque in masses) with a porcellanous lustre (masses), possesses a white streak, is brittle with a platy habit and has an uneven to conchoidal fracture. VHN₂₀₀ is 390 (range 343–426) kg/mm². Mohs’ hardness is 4–5. It shows weak pink-orange fluorescence under both short- and long-wave ultraviolet radiation. An infra-red adsorption spectrum is given and shows strong, sharp peaks at 3490 and 3418 cm^–1 which indicates that water is present as (OH) only. Peaks at 1409 and 1335 cm^–1 indicate the presence of BO₃ groups, and between 900 and 1180 cm^–1 the probable presence of BO₄. In transmitted light, plates and grains of jadarite show twinning in some crystallites and for 590 nm n = 1.536(± 0.001) and n = 1.563(± 0.001). It is non-pleochroic, biaxial, and does not show parallel extinction. In plane-polarized reflected light, the mineral is dark grey with weak bireflectance, it is non-pleochroic and has abundant white internal reflections. Wet chemical analysis combined with CHN analyzer gave the following aggregate composition: Li₂O 7.3, Na₂O 15.0, SiO₂ 26.4, B₂O₃ 47.2, H₂O 4.3, total 100.2 wt.%. The empirical formula, based on 3B atoms per formula unit (apfu), is: Li_1.08Na_1.07Si_0.97B₃O_6.99(OH)_1.06. Jadarite is monoclinic (P2₁/n) with a 6.818(2), b 13.794(2), c 6.756(2) Å, ß 111.10(2)° V 592.8(2) ų (Z = 4), alternatively (P2₁/c) with a 6.756(3), b 13.794(2), c 7.680(3) Å, ß 124.07(3) °, V 592.9(4) ų and Z = 4. The measured density (Berman Balance) is 2.45 g/cm³; calculated density is 2.46 g/cm³ (on the basis of the empirical formula and unit-cell parameters refined from powder data). The six strongest X-ray powder-diffraction lines [ in Å(I)(hkl)] are: 4.666 (62) (120, 021), 3.180 (82) (200), 3.152 (74) (002), 3.027 (40) (221), 2.946 (100) (131), 2.241 (74) (3 11,151), The mineral name is for the locality in Serbia where it was discovered during mineral exploration of the Jadar Basin.

Key-words: jadarite, new mineral species, lithium sodium borosilicate hydroxide, Jadar Basin, Serbia, chemical data, infra-red absorption spectrum, X-ray powder-diffraction data.