NATURAL KIND CLUSTERING OF PLANETARY MATERIALS: A NEW DATA-DRIVEN APPROACH TO MINERAL CLASSIFICATION

Minerals reveal the nature of the co-evolving geosphere and biosphere through billions of years of Earth history. Mineral classification systems have the potential to elucidate this rich evolutionary story; however, the present mineral taxonomy, based as it is on idealized major element chemistry and crystal structure, lacks a temporal aspect and thus cannot reflect planetary evolution. A complementary system of mineralogy can be based on quantitative analysis of large and growing mineral data resources by “natural kind clustering.” This approach to classification has the potential to amplify, though not supercede, the present classification system. A new system of mineralogy is especially important in mineral evolution and ecology, which examine the diversity and distribution of minerals through time and space. We ask how many different kinds of minerals occur on Earth? Does that number change through time? How does that number on Earth compare to other (typically less well endowed) planets and moons, both in our solar system and beyond? And by what natural physical, chemical, and biological processes do new minerals arise? These questions of mineral diversity and planetary evolution cannot be fully resolved using the IMA criteria for differentiating mineral species for at least three reasons: (1) some distinct natural kinds have been lumped in the IMA classification; (2) some individual natural kinds have been split by the IMA classification; and (3) a variety of important noncrystalline materials are not incorporated in the present system. A complementary division of condensed planetary materials into natural kinds based on observed ranges of chemical and physical characteristics of any natural condensed phase will reflect not only a substance’s major element chemistry and crystal structure, but also the physical, chemical, and/or biological process by which it formed.