ABSTRACT The ree-ont ontology formally represents the semantics of the complex interactions in the rare-earth elements (REE) mineral system from a self-organized criticality perspective. This ontology models various primarily heat-driven, melt-led, ore-forming processes that contribute to the formation of the REE-bearing alkaline intrusive bodies and related hydrothermal deposits. It also models the processes that form sediment-hosted concentrations of the REE from the weathering and erosion of the primary REE deposits. The ontology explicitly formalizes the interactions among the members of various magmatic, hydrothermal, basinal, regolith, and supergene subsystems. It represents the principal geodynamic, tectonic, and geological driver, trigger, carrier, conduit, and barrier roles that the components of the REE mineral system recursively play in enriching the REE during the subcritical and critical stages of the evolution of the complex system in and on the surface of the Earth’s crust. ree-ont establishes a logical machine processable basis for understanding the dynamic interactions among various components of the REE mineral system by extending the upper-level Basic Formal Ontology (BFO) and its underlying mid-level Common Core Ontologies (CCO).