Mineral evolution posits that Earth’s near-surface mineral diversity gradually increased through chemical and biological processes. A dozen different species in interstellar dust particles that formed the solar system have evolved to more than 4500 species today. Previous work demonstrated that up to two thirds of the known mineral species on Earth are linked to biological activity—including most of approximately 90 mercury minerals. New work published in American Mineralogist  demonstrates that most mercury mineralization occurred in the past 3 billion years during three periods of supercontinent assembly, as a consequence of continental collision and mineralization associated with mountain formation.
By contrast, few Hg minerals formed during periods when supercontinents were stable, or when they were breaking apart. In one striking exception to this trend, the billion-year-long interval that included the assembly of the Rodinian supercontinent (approximately 1.8 to 0.8 billion years ago) saw no mercury mineralization anywhere on Earth. Hazen and his colleagues  speculate that this hiatus could have been due to a sulfide-rich ocean, which quickly reacted with any available mercury and thus prevented mercury from interacting chemically with other elements.
The role of biology is also critical in understanding the mineral evolution of mercury. Although mercury is rarely directly involved in biological processes its interactions with oxygen came about entirely due to the appearance of the photosynthetic process, which plants and certain bacteria use to convert sunlight into chemical energy. Mercury also has a strong affinity for carbon-based compounds that come from biological material, such as coal, shale, petroleum, and natural gas products.
Photo: Cinnabar (HgS), RRUFF 070532, on calcite from Charcas, San Luis Potosi, Mexico. Courtesy of Robert Downs.