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volutionary theory states that some dif-ferences between individuals in a popu-lation are heritable, so that, when the environment changes, individuals bearing traits that provide the best adaptation to the new envi-ronment have the greatest chance for reproduc-tive success. In a recent article in the American Mineralogist (1), Hazen et al. apply the term “evolution ” to minerals in a similar manner, because new mineral patterns will adapt or evolve with changing environmental condi-tions throughout geologic time. The authors argue that the vast increase in the number of discrete mineral phases—from a sparse ~60 at the time of Earth’s formation to the more than 4300 known mineral species found on the modern Earth’s surface—requires an evo-lutionary explanation that goes beyond pure physical and chemical considerations. Hazen et al. define three eras comprising 10 stages, which relate mineral evolution to the chronological divisions of Earth’s history. The eras of Earth’s mineral evolution arise from three basic mechanisms: first, the gradual change in the concentration and distribution of elements from the presolar nebula homogeny to an expanded mineralogical diversity through physical processes during the era of planetary accretion (over 4550 million years ago); sec-ond, the introduction of new physicochemical conditions on the Earth’s surface, such as vari-able pressures and temperatures, as well as the increased activities of