TY - JOUR
T1 - The crystal structure of (Be,¿) (V,Ti)3O6, a mineral related to kyzylkumite
AU - Raade, Gunnar
AU - Balic Zunic, Tonci
PY - 2006
Y1 - 2006
N2 - The crystal structure of (Be,¿)(V,Ti)3O6, a mineral discovered in the emerald deposit of Byrud, Norway, has been solved and refined to R1 = 4.51% for 1413 unique reflections. 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, Mg3SiO4F2. 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(V3+1.27Ti1.21Cr0.29Fe0.08Al0.07)S2.92O6. The presence of Be was verified by the structure analysis and a SIMS analysis. The occupancy of the Be site was found to be 0.84(1), which largely explains the surplus of Ti in the empirical formula, as compared to the stoichiometric formula BeV2TiO6. However, there is no evidence for ordering of V and Ti on two unique octahedral sites of the structure. The amended empirical formula is (Be0.84¿0.16)(V3+1.32Ti1.25Cr0.29Fe0.09Al0.07)S3.02O6. 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 V2Ti3O9. The crystal-lattice parameters found earlier for kyzylkumite can be explained as based on an 8x supercell obtained on a {210} reflection twin. This type of twinning is characteristic for the Byrud mineral, and was 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 was also the main constituent of material described as kyzylkumite, which probably also contained additional phases, and that a redefinition of this mineral is needed.
AB - The crystal structure of (Be,¿)(V,Ti)3O6, a mineral discovered in the emerald deposit of Byrud, Norway, has been solved and refined to R1 = 4.51% for 1413 unique reflections. 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, Mg3SiO4F2. 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(V3+1.27Ti1.21Cr0.29Fe0.08Al0.07)S2.92O6. The presence of Be was verified by the structure analysis and a SIMS analysis. The occupancy of the Be site was found to be 0.84(1), which largely explains the surplus of Ti in the empirical formula, as compared to the stoichiometric formula BeV2TiO6. However, there is no evidence for ordering of V and Ti on two unique octahedral sites of the structure. The amended empirical formula is (Be0.84¿0.16)(V3+1.32Ti1.25Cr0.29Fe0.09Al0.07)S3.02O6. 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 V2Ti3O9. The crystal-lattice parameters found earlier for kyzylkumite can be explained as based on an 8x supercell obtained on a {210} reflection twin. This type of twinning is characteristic for the Byrud mineral, and was 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 was also the main constituent of material described as kyzylkumite, which probably also contained additional phases, and that a redefinition of this mineral is needed.
KW - Faculty of Science
KW - krystal strukturer
KW - Norge
KW - kyzylkumite
KW - V-Ti-Be oxide
KW - twin
KW - crystal structure
KW - leucophoenicite-humite series
KW - norbergite isotype
KW - Norway
KW - Byrud emerald deposit
KW - (Be,¿)(V,Ti)3O6
M3 - Journal article
SN - 0008-4476
VL - 44
SP - 1147
EP - 1158
JO - Canadian Mineralogist
JF - Canadian Mineralogist
ER -