Microscopy analysis of garnet from a metamorphic rock of the Santander Massif´s crystalline basement, Eastern Cordillera (Colombian Andes): Morphology as evidence of nucleation and growth

Abstract

This study focuses on the morphology of garnet from a metamorphic rock in the crystalline basement of the Santander Massif, Eastern Cordillera (Colombian Andes). We identify rough stepped surfaces on the {211} and {110} faces of the garnet. Using a combination of petrography, scanning electron microscopy (SEM), and atomic force microscopy (AFM), we examine these surface structures. Garnet from this region typically shows chemical zoning, but our samples are chemically homogeneous, likely due to diffusion during high-grade metamorphism. The garnet exhibits an anhedral to subhedral morphology, differing from its typical euhedral form, indicating unique formation conditions. SEM analysis reveals that the trapezohedron {211} and dodecahedron {110} faces have different growth rates and surface topographies. AFM confirms a faceted morphology with terraces, suggesting a layer-by-layer growth mechanism. Our findings provide insights into the nucleation and growth processes of garnet under varying physiochemical conditions, contributing to the broader understanding of metamorphic processes in the Santander Massif.