Abstract

Byrudite (IMA 2013-045, Raade et al., 2013), with simplified formula (Be,□)(V3+,Ti)3O6, occurs in emerald-bearing syenitic pegmatites of Permian age at Byrud farm, Eidsvoll, Akershus, South Norway. It has a norbergite-type structure, Pnma, with a = 9.982(1), b = 8.502(1), c = 4.5480(6) Å, V = 385.97(9) Å3, Z = 4. The structure was refined to R1 = 0.045 for 1413 unique reflections. Twinning occurs on {210}. The occupancy of the tetrahedral Be site refined to 0.84(1). The presence of Be was verified by secondary ion mass spectrometry but could not be quantified. Electron-microprobe analyses of the crystal used for structure determination gave the empirical formula (Be0.840.16)(V1.323+Ti1.25Cr0.29Fe0.09Al0.07)Σ3.02O6. There is a strong inverse correlation between V and Cr. The ideal endmember formula is BeV23+TiO6. The mineral is black and opaque with a metallic lustre. Reflectance data in air are reported from 400 to 700 nm. The Commission on Ore Mineralogy required wavelengths are [R1,R2(λ in nm)]:16.6,17.5(470), 16.7,17.9(546), 16.8,18.3(589) and 16.8,18.6(650). The Mohs hardness is ~7, based on indentation measurements. The mineral is brittle with an uneven fracture; cleavage is not present. D(calc.) = 4.35 g cm−3 for the empirical formula with 0.84 Be a.p.f.u. The strongest reflections of the calculated powder X-ray diffraction pattern are [d in Å(Irel)(hkl)]: 3.721(72)(111), 2.965(100)(121), 2.561(50)(311), 2.464(41)(230), 2.167(24)(231), 1.681(34)(402), 1.671(66)(232), 1.435(23)(630).

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