Strontiohurlbutite, SrBe2(PO4)2, a new mineral from Nanping No. 31 pegmatite, Fujian Province, Southeastern China.

Strontiohurlbutite, ideally SrBe₂(PO₄)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), γ = 1.572(3) (white light), 2V_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, P₂O₅ 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_0.81Ca_0.05Ba_0.01)_Σ0.87Be_2.02P_2.05O₈. 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)(321); 2.046(54)(223); 1.714(32)(143). Strontiohurlbutite is monoclinic, space group P2₁/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) ų (Z = 4, calculated density = 3.101 g/cm³). The mineral is isostructural with hurlbutite, CaBe₂(PO₄)₂, and with paracelsian, BaAl₂Si₂O₈. The formation of strontiohurlbutite is related to the hydrothermal alteration of primary beryl by late Sr- and P-rich fluids. [ABSTRACT FROM AUTHOR]