Naslov
Montmorillonite alteration of tourmaline from the Quintos de Baixo pegmatite, Borborema Pegmatite Province, NE Brazil

Autori
Strmić Palinkaš, Sabina ; Bermanec, Vladimir ; Žigovečki Gobac, Željka ; Palinkaš, Ladislav Antun ; Kampić, Štefica ; Wegner, Reinhard ; Odúlio, José Marensi Moura

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Acta mineralogica-petrographica, Abstract series, Volume 6 (special selection) MECC2010 / Zaharia, Luminiţa, Kis, Annamária, Topa, Boglárka, Papp, Gábor, Weiszburg, Tamás G. - Segedin : University of Szeged, 2010, 99-99

Skup
5th Mid-European Clay Conference (MECC2010)

Mjesto i datum
Budimpešta, Mađarska, 25.08.2010. - 29.08.2010

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
tourmaline; Quintos de Baixo pegmatite; montmorillonitic alteration

Sažetak
Tourmaline is a common boron-rich mineral in granitic pegmatites. It is resistant to weathering and typically occurs as a detrital mineral in sedimentary rocks and soils. However, tourmaline in pegmatites may be partially altered to various aluminous minerals. Alterations are mostly associated with late magmatic and hydrothermal fluids. Tourmaline from the Quintos de Baixo pegmatite, Borborema Pegmatite Province, NE Brazil, displays zonal structure with Li-Al-rich core (elbaite) and Fe-rich rim (schorl). The core is frequently altered to clay minerals. Matrix between tourmaline crystals comprises clay minerals as well. According to X-ray powder diffraction (XRPD) analysis the principal clay mineral is montmorillonite with cation exchange capacity (CEC) of 75.5 ± 0.4 mEq/100g. The following reaction illustrates breakdown of tourmaline (elbaite) into Li-montmorillonite: Na(Li, Al)3Al6(BO3)3Si6O18(OH)4 + 5H4SiO4 + 3H+ ↔ 3[Al3(Si3.67Al0.33)O10(OH)2]Li0.33 + 3H3BO3 + 2Li+ + Na+ + 6H2O (rG0 = -69.7 kcal/mol). The reaction requires increased activity of H4SiO4 and points to the influence of late magmatic or hydrothermal fluids. Alternatively, the weathering of spodumene can represent an important source of montmorillonite: 7LiAlSi2O6 + 6H+ + 6H2O ↔ 3[Al3(Si3.67Al0.33)O10(OH)2]Li0.33 + 3H4SiO4 + 6Li+ (rG0 = -2.6 kcal/mol) Gibbs free energies for above mentioned reactions (rG0) have been estimated according to the thermodynamic data published by Woods & Garrels (1987), Tardy & Garrels (1974) and Ogorodova et al. (2004).

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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