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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEÅž-BOLYAI
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Rezumat: Vashegyite, ideally Al11(PO4)9(OH)6•38H2O or Al6(PO4)5(OH)3•23H2O, occurs as dull (chalky) white irregular nodules up to 1.5-2.5 cm in diameter within the fresh guano deposit from the Gaura cu Muscă Cave (Locvei Mountains, SW Romania). It is friable and usually covered by a millimeter-size sandy clay film. It was characterized by means of X-ray diffraction, thermal, scanning electron microscope (SEM-EDS), infrared spectroscopy, and by chemical analysis. Under SEM, vashe-gyite shows euhedral and subhedral crystals (up to 10 m across) flattened on (001) with {010} and {001} being the prominent forms. An EDS inspection of the vashegyite crystals surface indicate the presence of the following elements: Al, P, Si, S, and Fe.
Indexing of the X-ray powder pattern (Philips X-pert, CuK radiation) gave orthorhombic symmetry with the following calculated parameters are a = 10.75(6), b = 15.029(9), c = 22.444(5) Å, and V = 3626.433(4) Å3; strongest lines are 11.21 (100, 002), 7.52 (77, 020), 6.9 (28, 112), 6,25 (72, 022), 3.297 (40, 312), 2.909 (60, 330), and 2.44 (15, 062).
Vashegyite IR absorption bands are comparable in position and relative intensity to bands in the spectra of other Al phosphates (variscite, wavellite, etc.). The most important absorption bands (cm-1) are at 3400 and 3200 (H2O, OH stretching), 1635 (H2O bend), 1384 (OH ), 1165, 1115, 1007 (PO4: 3, antisymmetric stretching), 729 (Al-OH2 mode or OH out-of-plane band), 603, 525, 482 (PO4: 4, in-plane bending).
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