metallicity

This term is a specialized technical descriptor used almost exclusively in astrophysics and stellar evolution. It does not refer to the quality of being metallic in a general sense, but specifically quantifies the ratio of heavy elements to hydrogen and helium within a celestial body.

Because it describes a chemical proportion or a state of enrichment, it functions as an uncountable mass noun. It is typically measured on a logarithmic scale, meaning that a small numerical change in metallicity represents a significant difference in the actual chemical composition of a star.