Crystallization via Nonclassical Pathways: Nanoscale Imaging of Mineral Surfaces
Christine V. Putnis, Lijun Wang, Encarnación Ruíz-Agudo, Cristina Ruiz‐Agudo, François Renard
Abstract
The advancement in analytical imaging techniques, including atomic force microscopy and scanning and transmission electron microscopies, has allowed us to observe processes occurring at mineral surfaces in situ at a nanoscale in real space and time, hence giving the possibility to elucidate reaction mechanisms. Classical crystal growth theories have been established for well over 100 years, and while they can still be applied to explain crystal growth in many growth scenarios, we now know that these models are not always an accurate description of the mechanism of all crystal or mineral growth processes, especially where nanoparticle formation is observed. Consequently, there is a current challenge at the forefront of understanding crystal or mineral growth mechanisms. The work in this chapter describes experimental observations of nonclassical crystallization processes at the nanoscale. Using atomic force microscopy as well as scanning electron microscopy and transmission electron microscopy imaging, we demonstrate that a diverse range of minerals grows by the attachment of nanoparticles on a growing mineral surface. Through extensive and varied examples of crystal or mineral growth, including calcite and other carbonates, barite, brucite, and apatite, we define the importance of the mineral-fluid interface and the aqueous fluid interfacial (boundary) layer in the control of crystal growth. Whether a crystal will grow by classical monomer attachment, which results in step advancement, or by the formation, aggregation, and merging of nanoparticles, it will be controlled by the aqueous fluid composition at the mineral-fluid interface.