Crystalline fabrics of secondary gypsum after glauberite replacement: utility for sodium sulphate prospection

Many sodium sulphate formations deposited during the Miocene in the sedimentary basins of the Iberian Peninsula are currently exposed to the weathering action on the surface or dose subsurface. A common replacement product of glauberite in these formations is secondary gypsum. This type of gypsum very frequently preserves extensive pseudomorphic lithofacies inherited from the glauberite precursors, and also typically displays some particular crystalline fabrics (reticulate, acicular) which characterize this replacement process. Both the pseudomorphic (macroscopic) lithofacies and the microscopic textures may be used togheter as diagnostic features in geological prospecting of surficially weathered sodium sulphate formation