gems, beryl, emerald, geology

Giuliani and colleagues present a genetic classification of emerald deposits based on the geological processes that bring beryllium into contact with chromium and/or vanadium, the elements principally responsible for emerald coloration. The authors distinguish two major types: tectonic-magmatic-related deposits, in which Be-bearing magmatic or hydrothermal fluids interact with Cr- and V-bearing rocks, and tectonic-metamorphic-related deposits, in which emerald formation is associated principally with metamorphic and tectonic processes without a direct magmatic contribution. These types are subdivided according to host rocks and geological environment, encompassing deposits associated with mafic-ultramafic rocks, sedimentary rocks, and other metamorphic settings. Representative emerald deposits from around the world illustrate the classification and demonstrate the diverse geological mechanisms capable of overcoming the unusual geochemical separation of beryllium from chromium and vanadium. The chapter provides a concise framework for comparing the geology, genesis, and worldwide distribution of emerald deposits.