| Autor: |
Strmić Palinkaš, Sabina, Bermanec, Vladimir, Žigovečki Gobac, Željka, Palinkaš, Ladislav Antun, Kampić, Štefica, Wegner, Reinhard, Odúlio, José Marensi Moura |
| Přispěvatelé: |
Zaharia, Luminiţa, Kis, Annamária, Topa, Boglárka, Papp, Gábor, Weiszburg, Tamás G. |
| Jazyk: |
angličtina |
| Rok vydání: |
2010 |
| Předmět: |
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| Popis: |
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). |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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