Original paper
Berborite polytypes
Giuseppetti, G.; Mazzi, F.; Tadini, C.; Larsen, A. O.; Åsheim, A.; Raade, G.
Neues Jahrbuch für Mineralogie - Abhandlungen Band 162 Heft 1 (1990), p. 101 - 116
13 references
published: Sep 11, 1990
DOI: 10.1127/njma/162/1990/101
ArtNo. ESP154016201005, Price: 29.00 €
Abstract
Three polytypes of berborite, Be2(BO3)(OH) • H2O, are described from nepheline syenite pegmatites of the Saga larvikite quarries, Tvedalen district, southern Oslo region, Norway. Berborite-1T (similar to type berborite from Pitkäranta, Karelian SSR) has space group P3; cell parameters from single-crystal data are a = 4.434(1), c = 5.334(2) Å. Its crystal structure was refined to R = 0.014. Berborite-2T has space group P3c1; a = 4.431(1), c = 10.663(3) Å; R = 0.019. The measured density is 2.06 ± 0.01g/ cm3; refractive indices are ω = 1.5817(3), ε = 1.4884(2) (for 589 nm). Berborite-2H has space group P63; a = 4.433(2), c = 10.638(5) Å; R = 0.029. Measured density 2.03 g/cm3; ω = 1.5804(5), ε = 1.4928(2). The crystal morphologies of the three polytypes are outlined, and calculated and observed X-ray powder data are given. It was found for all polytypes that the Be-atoms and the O(2) apical oxygens of the Be-tetrahedra are split into two non-equivalent sites. Water and hydroxyl oxygens are ordered on separate O(2) positions.
Keywords
Berborite • polytypes • crystal morphology • X-ray powder data • crystal structures; Norway (Saga • Tvedalen • Oslo region)