Crustales

Crustales are a term used in speculative geology and some science-fiction contexts to describe a class of crystalline coatings that form crust-like shells on mineral surfaces. The term is not widely established in mainstream geology, and definitions vary between sources. In many usages, crustales refer to thin, coherent layers of crystals that encrust grains or rocks, sometimes persisting after the underlying material has weathered or altered.

Formation and properties: Crustales are described as forming when mineral-rich fluids or vapors precipitate crystals along exposed surfaces, creating a crust with a mineralogy that can differ from the substrate. They may develop through surface crystallization under conditions of low temperature or hydrothermal activity, and their thickness can range from micrometers to millimeters. Textures are typically sheet-like, radial, or polycrystalline, and the coatings may exhibit distinct optical effects such as iridescence in some depictions.

Composition and variability: Depending on the environment, crustales are imagined to consist of silicates, carbonates, oxides, or sulfides. In fiction, their appearance and properties are often tailored to story needs, sometimes described as unusually hard, light, or translucent.

Occurrence and research: In current scientific literature, crustales are not recognized as a distinct natural mineral class. They appear mainly as a hypothetical concept or as a modeling tool to study surface crystallization, coating processes, or diffusion-limited growth. Experimental analogs in laboratories can recreate crust-like coatings under controlled conditions, providing insight into coating dynamics and crust formation.

Etymology and use: The name derives from the crust-like appearance of the coating. In cultural contexts, crustales serve as a device in worldbuilding and speculative design to illustrate crust-forming phases in planetary or extraterrestrial environments.