ALBERT

Description: Strontiohurlbutite, ideally SrBe 2 (PO 4 ) 2 , is a new member of hurlbutite group discovered in the Nanping No. 31 pegmatite, Fujian province, southeastern China. Crystals are mainly found in zones I, II, and IV; they are platy, subhedral-to-anhedral, with a length from 5 μm to 1.5 mm. Associated minerals mainly include quartz, muscovite, beryl, hurlbutite, hydroxylherderite, apatite-group minerals, and phenakite. Strontiohurlbutite crystals are light blue, translucent-to-transparent, and have vitreous luster. The Mohs hardness is about 6, and the tenacity is brittle. Optically, strontiohurlbutite is biaxial (–), α = 1.563(3), β = 1.569(2), = 1.572(3) (white light), 2 V meas = 68.5(5)°, and exhibits weak dispersion, r 〉 v. The optical orientation is X = b , Y c . Electron-microprobe and SIMS analyses (average of 16) give SrO 29.30, P 2 O 5 51.05, CaO 0.91, BaO 0.64, and BeO 17.71 wt%; total 99.61 wt%. The empirical formula, based on 8 O apfu, is (Sr 0.81 Ca 0.05 Ba 0.01 ) 0.87 Be 2.02 P 2.05 O 8 . The stronger eight lines of the measured X-ray powder-diffraction pattern [ d in Å( I )( hkl )] are: 3.554(100)(121); 3.355(51)(211); 3.073(38)(022); 2.542(67)(113); 2.230(42)(213); 2.215(87)(32); 2.046(54)(223); 1.714(32)(143). Strontiohurlbutite is monoclinic, space group P 2 1 / c ; unit-cell parameters refined from single-crystal X-ray diffraction data are: a = 7.997(3), b = 8.979(2), c = 8.420(7) Å, β = 90.18(6)°, V = 604.7(1) Å 3 ( Z = 4, calculated density = 3.101 g/cm 3 ). The mineral is isostructural with hurlbutite, CaBe 2 (PO 4 ) 2 , and with paracelsian, BaAl 2 Si 2 O 8 . The formation of strontiohurlbutite is related to the hydrothermal alteration of primary beryl by late Sr- and P-rich fluids.

Description: Mengxianminite, ideally Ca 2 Sn 2 Mg 3 Al 8 [(BO 3 )(BeO 4 )O 6 ] 2 , is a new borate mineral from Xianghualing skarn, Hunan Province, southern China. It occurs in the hsianghualite vein of Xianghualing skarn, associated with fluorite, phlogopite, hsianghualite, magnetite, dravite, magnesiotaaffeite-2 N '2 S , and calcite. Mengxianminite forms subhedral to euhedral green crystals from 20 to 200 μm long, translucent to transparent, with a vitreous luster. The crystals show perfect cleavage on {100} and good cleavage on {010}, and do not fluoresce in long- or short-wave ultraviolet light. The estimated Mohs hardness is 8, and the tenacity is brittle with irregular fracture. The calculated density is 4.170 g/cm 3 . Optically, mengxianminite is biaxial (–), with α = 1.80(2), β = 1.83(2), = 1.84(2) (589 nm). The mean chemical composition of mengxianminite is Al 2 O 3 40.00, SnO 2 25.96, MgO 6.57, CaO 8.56, FeO 4.83, B 2 O 3 6.53, BeO 4.37, ZnO 1.81, MnO 1.23, Na 2 O 1.13, TiO 2 0.10, SiO 2 0.04, sum 101.12 with a corresponding empirical formula calculated on the basis of 26 O atoms of (Ca 1.64 ,Na 0.39 ) 2.03 (Sn 1.85 ,Zn 0.24 ) 2.09 (Mg 1.75 , Fe 0.72 ,Al 0.42 ,Mn 0.19 ,Ti 0.01 ) 3.09 Al 8 [(B 1.01 O 3 )(Be 0.94 O 4 )O 6 ] 2 . (Be and B were measured by secondary ion mass spectrometry, average of six electron microprobe analyze points and in wt%.) The strongest eight lines of the powder XRD pattern [ d in Å ( I )( hkl )] are: 3.000 (35)(16.2.0); 2.931 (100)(17.1.1); 2.475 (29)(022); 2.430 (30)(13.3.1); 2.375 (100)(14.0.2/640); 2.028 (52)(21.3.1); 1.807 (35)(913); 1.530 (98)(14.6.0/15.3.3). Mengxianminite is orthorhombic, space group Fdd 2; unit-cell parameters refined from single-crystal X-ray diffraction data are: a = 60.699(4), b = 9.914(1), c = 5.745(1) Å, V = 3457.4(4) Å 3 , and Z = 8. The structure of mengxianminite is characterized by the alternating O-T1-O-T2-O'-T2 layers stacked along the a axis, which are equal to two alternating modules: the module A (O-T1-O) corresponding to the spinel module with an additional O layer (AlO 6 octahedra layer), and the module B (T2-O'-T2) showing the simplified formula CaSnAl(BeO 4 )(BO 3 ), where SnO 6 octahedra are isolated in the T2 layers, connected via BeO 4 and CaO 11 groups, and AlO 6 edge-sharing octahedra in the O' layer form chains running along the {011} or {01} direction, connected in the c direction by the BO 3 triangular groups. Mengxianminite is the first borate mineral with both Sn and Be, likely crystallized under F-rich conditions at late stages of the Xianghualing skarn.