Experimental epitaxial nucleation and growth of zeolites in basalt minerals

Abstract

Zeolites are secondary minerals common in volcanic rocks, widely distributed in the basalts of the Paraná Magmatic Province (PMP). Cavities in volcanic rocks are usually filled by complex secondary mineralogical assemblages, with several species of zeolites, in addition to chlorite, apophyllite, quartz, and calcite. Several authors have sought to correlate crystallization sequences of zeolites and other secondary minerals with the evolution of post-magmatic hydrothermal systems since zeolite diversity reflects the evolution of the chemical composition and temperature of hydrothermal fluids, as can be seen in the works on basalts of the Paraná Basin, Brazil (Murata, Formoso and Roisenberg, 1987; Schenato et al., 2003), Hvalfjördur Area, Iceland (Weisenberger and Selbekk, 2009) and Kaiserstuhl Volcanic Complex, Germany (Weisenberger, Spürgin and Lahaye, 2014). The mineralogical diversity of zeolites in the same cavity suggests that the free energy variations between different zeolite species are small. This hypothesis has been suggested since the pioneering works on zeolite synthesis. Barrer et al. (1959, apud Cundy and Cox, 2005) suggested that zeolites probably crystallize from structural elements formed in solution and combined in different ways to produce the different species. A possibility not considered so far is the influence of the epitaxial effect on the crystallization of zeolite species. This possibility will be experimentally tested in the present project. Hydrothermal zeolite synthesis will be performed using pure compounds and solutions containing SiO2 and Al2O3 and hydroxides of Ca and Na, will be seeded with plagioclase (labradorite), clinopyroxene (augite or diopside), chlorite, and basalt powder, in order to observe the possible influence of the substrate on the zeolite formation. The control of the experimental products will be done by X-ray diffraction and scanning electron microscope. Computational simulations will be done with crystal structure projection programs. (AU)