MINERAL EVOLUTION: DRIVING FORCES AND PROSPECTS FOR FUTURE RESEARCH

Fundamentally, mineral evolution has been driven by two factors. First, the initial relatively uniform distribution of mineral-forming elements in the early solar system has differentiated to the extent that even rare elements can be concentrated enough to form minerals in which they are major constituents. Second, the ranges of environmental parameters such as pressure (P), temperature (T), and the activity of volatiles, like H₂O, CO₂, and O₂, have increased over the history of the Earth. The formation of a new mineral is a function of the chemical composition of the growth medium, P, T, and volatile activities, and governed by energy minimization. Thus, the effect of one factor in creating new minerals amplifies the effect of the other. Processes that have caused chemical differentiation and concentration of elements are familiar subjects in geology and petrology such as core formation, fractional crystallization of silicate melts, fractional melting of rocks, evaporation of seawater, sediment transport by river and ocean currents, and biological activity. Processes that have caused diversification of environmental parameters are likewise familiar, including planetary accretion, meteorite impacts, plate tectonics, fluid separation from magma, contact metamorphism, fluid-rock interaction, and arguably most important, biological activity.

The history of first appearances of minerals on Earth remains largely uncharted in detail. Progress will be impeded by the uncertain interpretation of the ages of many mineral species that have a single or only a few occurrences. Mineral evolution has a brighter future in research if the concept is expanded to consider the evolution of mineral compositions (elemental and isotopic), mineral associations, and mineral abundances. Without invoking the term mineral evolution, recent studies, for example, have already made groundbreaking discoveries about Earth history by tracking secular changes in the sulfur isotope composition of sulfides and sulfates, the oxygen isotope composition and Th/U of zircon, and the distribution of aragonite and calcite in marine sediments. The banner of mineral evolution can help lead to further important discoveries by focusing attention on the change of all aspects of mineralogy throughout geologic time.