At Baita Bihor (formerly Rezbanya), Romania, the type locality szaibelyite occurs in magnesian skarns hosted by the dolomitic marbles of Mesozoic age, near the contact with a granite - granodiorite body of Upper Cretaceous - Paleogene age. Associated minerals include calcite, dolomite, magnesite, kotoite, suanite, ludwigite, fluoborite, fluorite, chondrodite. norbergite, magnetite, brucite, chrysotile, lizardite, clinochlore, lepidocrocite and goethite. Szaibelyite from B aita Bihor is extremely close to the end-member composition [Mg-2(B2O4OH)(OH)]. Up to 0.88 mol.% sussexite (the Mn end-member), 1.06 mol.% Fe-2(B2O4OH)(OH) and 0.20 mol.% Ca-2(B2O4OH)(OH) may be deduced on the basis of combined wet-chemical and electron-microprobe analyses. The mineral exhibits very slight fluorine contents [X-F = F/(F + OH)< 0.01]. Selected area electron imaging supported by X-ray powder patterns indicate that the szaibelyite from Baita Bihor is monoclinic, space group P2-l/a. The mean unit-cell parameters are a 12.559(18), b 10.402(12). c 3.132(8)
and beta 95.77(33)degrees. Thermogravimetric curves gave a smooth and continuous weight loss of up to 3.39 wt.% H2O between 150 and 600 degreesC, in reasonable agreement with the results obtained by loss on ignition. The complete dehydration occurs between 650 and 700 degreesC, the breakdown product being the monoclinic (P2(1)/a) polymorph of Mg-2(B2O5) Two OH-stretching bands in the infrared absorption spectra of the mineral, at similar to 3560 and similar to 2510 cm(-1), respectively, are indicative of two distinct hydrogen positions in the structure. The IR spectra do not systematically show absorption systematically at similar to 1630 cm(-1) (bending mode of H2O), suggesting that the mineral does not contain molecular H2O. Szaibelyite from Baita Bihor is estimated to have developed at temperatures of 160-450 degreesC. pressures of 0.6-3 kbar, at relatively high activity of fluorine, and at low potentials of iron and manganese.