The structure of the new disilicate kristiansenite, Ca

The crystal structure of (Be,Ⅺ)(V,Ti) 3 O 6 , a mineral discovered in the emerald deposit of Byrud, Norway, has been solved and refi ned to R 1 = 4.51% for 1413 unique refl ections. The structure is orthorhombic, Pnma, with lattice parameters a 9.982(1), b 8.502(1), c 4.5480(6) Å, Z = 4, and isotypic with norbergite, Mg 3 SiO 4 F 2 . The empirical chemical formula, based on the electron-microprobe determination of elements heavier than oxygen, and beryllium tentatively calculated to give 1Be for O = 6, is Be(V 3+ . The appearance of the mineral, the dominance of V and Ti in its composition, and the X-ray powder-diffraction data correspond to those described originally for kyzylkumite, supposed to be V 2 Ti 3 O 9 . The crystal-lattice parameters found earlier for kyzylkumite can be explained as based on an 8ϫ supercell obtained on a {210} refl ection twin. This type of twinning is characteristic for the Byrud mineral, and is present in the crystal used for the structure determination. These facts suggest that the same type of oxide of Be, V and Ti found at Byrud is also the main constituent of material described as kyzylkumite, which probably also contains additional phases, and that a redefi nition of this mineral is needed.Keywords: kyzylkumite, (Be,Ⅺ)(V,Ti) 3 O 6 , norbergite isotype, leucophoenicite-humite series, crystal structure, twin, V-Ti-Be oxide, Byrud emerald deposit, Norway. SOMMAIRENous avons résolu et affi né la structure cristalline de (Be,Ⅺ)(V,Ti) 3 O 6 , un minéral découvert dans le gisement d'émeraude de Byrud, en Norvège, jusqu'à un résidu R 1 de 4.51% en utilisant 1413 réfl exions uniques. La structure est orthorhombique, Pnma, avec les paramètres réticulaires a 9.982(1), b 8.502(1), c 4.5480(6) Å, Z = 4, et isotypique de celle de la norbergite, Mg 3 SiO 4 F 2 . La formule chimique empirique, fondée sur une détermination de la teneur en éléments plus lourds que l'oxygène, et le béryllium provisoirement fi xé à un atome de Be pour six d'oxygène, serait Be(V . L'apparence du minéral, la dominance de V et Ti dans sa formule, et les données de diffraction X (méthode des poudres) correspondent à ce qui a été antérieurement proposé pour la kyzylkumite, supposée être V 2 Ti 3 O 9 . Les paramètres réticulaires proposés pour la kyzylkumite témoignent d'une supermaille 8ϫ, résultat d'une macle par réfl exion sur {210}. Ce genre de macle est aussi caractéristique de notre minéral de Byrud, et il est aussi présent dans le cristal utilisé pour établir la structure. Ces faits font penser que la même sorte d'oxyde de Be, V et Ti découverte à Byrud est le composant principal du matériau décrit comme kyzylkumite, qui contient probablement des phases additionnelles. Il semble évident qu'une redéfi nition de la kyzylkumite s'impose.(Traduit par la Rédaction) Mots-clés: kyzylkumite, (Be,Ⅺ)(V,Ti) 3 O 6 , isotype de norbergite, série leucophoenicite-humite, structure cristalline, macle, oxyde de V-Ti-Be, gisement d'émeraude de Byrud, Norvège. §

No abstract

SUMMARY. Ktenasite from Glomsrudkollen zinc mine, Modum, Norway, is menoclinic, space group P21/c.The cell dimensions are a 5'598, b 6.121, c 23'762/~, /5 95.55 ~ The chemical formula is (Cu3.sZnl.5)(SO4)~ (OH)n.6H20 with Z = 2; Pcale 2"96 g/cm 3, Pobs 2"94 g/cm 3. The mineral is biaxial negative with ~ (colourless) 1'574,/5 (bluish green) 1'615, v (light green) 1.628, 2V~ 59 ~ KTENASITE was originally described by Kokkoros (195o) from the Kamariza mine, Laurium, Greece, where it occurs sparingly as blue-green, platy crystals up to I mm, in association with smithsonite, glaucocerinite, and serpierite. The symmetry of ktenasite, determined by Weissenberg studies, is monoclinic, space group P21/c. Kokkoros concluded from a partial microchemical analysis on 2"5 mg (Table II) that the mineral is a sulphate of copper and zinc with the formula (Cu,Zn)~SO4(OH)4.2H20; there was, however, poor agreement between the observed and calculated densities.No other well-established occurrence of ktenasite seems to be reported in the literature. Ktenasite is mentioned by Rankin (1969) from the Ecton mine, Montgomery County, Pennsylvania, but no data are given and there must be doubt as to the identification.In I972 a green, platy mineral was detected by amateur collectors on material from the Glomsrudkollen zinc mine, Modum, Norway. It was subsequently identified as ktenasite by Raade, who also noted that Kokkoros's X-ray powder data were obtained on impure material. Some of the Norwegian ktenasite was later sent to Dr. A. Livingstone, Edinburgh, who, because of poor agreement with the published X-ray powder data, asked the British Museum (N.H.) for assistance. A description of this mineral is the subject of the present paper. Specimens are deposited in the British Museum (N.H.), London, the Mineralogical-Geological Museum, University of Oslo, and in the Royal Scottish Museum, Edinburgh.Occurrence. Glomsrudkollen mine is a contact deposit between quartz porphyry and limestone, situated within the Oslo Region (Goldschmidt, 191 I). The dump at the entrance of the lowest adit, now partly removed, was locally rich in sulphides, mainly sphalerite, pyrite, and chalcopyrite. Rock and mineral fragments of the dump were commonly cemented to a sort of breccia by secondary sulphates, mainly gypsum. In some places ktenasite occurred rather abundantly as aggregates of thin platy crystals or laths up to I ram, often growing on, and thus younger than, clear gypsum crystals. A thin coating of a pale blue mineral, shown by microchemical tests to be a Cu-Zn-A1 sulphate, has so far not been identified. Its X-ray powder pattern has broad and diffuse lines; scanning electron micrographs reveal an aggregate of platy crystals.The ktenasite-bearing material appeared when the dumps were taken out for road filling. Temporarily, large amounts of bianchite were seen to have precipitated as a white powder 9