Naica’s Giant Crystals: Characterization and Evolution of the Wall–Crystal Interface

Abstract

Naica’s “Cueva de los Cristales” (Cave of the Crystals) has been compared to the most beautiful places of worship for the incredible display of columns that populate its vault. Said columns are giant gypsum crystals that have already been the subject of extensive studies. This paper contributes to these studies by focusing on the mineral aggregates found at the wall–selenite interface. A detailed chemical and structural characterization of representative samples has been performed using chemical, mineralogical, elemental, and phase analysis methods, with an emphasis on synchrotron micro-spectroscopic techniques. The following main phases were identified: calcite, silica, goethite, and several Pb-, Mn-, Cu-, and Zn-based aggregates. The role of the mineral aggregates, from their potential incorporation at the very beginning of the formation to the final steps of the crystals’ growth, is investigated. Particular attention is paid to their shapes and composition. The data obtained on the morphology of the wall–crystal interface and related phase composition, together with classical nucleation formalisms based on the slightly supersaturated solution, suggest that the nanocrystalline monomers formed in solution undergo adsorption on the wall, which ultimately promotes mega crystal growth.