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On the Evolution of Minerals Minik T NEWS & VIEWS NATURE|Vol 456|27 November 2008 EARTH SCIENCE On the evolution of minerals Minik T. Rosing The variety of mineral species has increased since the birth of the Solar System and the development of terrestrial planets. A refreshing view likens the steady rise in mineral diversity to biological evolution. The 94 naturally occurring chemical elements that never travelled far from their starting can combine into an endless number of com- composition are ‘primitive’. The planets were pounds. In nature, however, such compounds constructed from building blocks similar to come as a few thousand mineral species1, each the meteorites that fall to Earth from time to with its own eclectic selection of atoms system- time. The meteorites, in turn, are composed of atically organized in crystal lattices. Geologists grains that condensed out of the solar nebula have long used the concepts of ‘primitive’ and or formed from melt droplets that circled the ‘evolved’ rocks to describe the observation that early Sun. The transition from primary dust planets such as Earth started out as more or to full-scale worlds was followed by a steady less homogeneous systems, which over time increase in mineral species diversity. segregated into chemically distinct reservoirs Writing in American Mineralogist, Hazen — on Earth, the continents, the oceans and et al.2 cast the progressive diversification of the atmosphere, for example. The rocks that the mineral inventory of the Solar System and differ most markedly from the initial average Earth (and presumably of the terrestrial planets planetary composition are ‘evolved’, and those in general) in terms of mineral evolution. They 456 NATURE|Vol 456|27 November 2008 NEWS & VIEWS Box 1 | A mineral selection OM y.c IBRAR l oto h/ph monteat . ROSING; c. ROSING; . T . ROSING; M. ROSING; . T M. Shown here are just three the newborn Sun. The colours small amounts of uranium. Over a highly systematic arrangement examples from the wide world of are not true, but result from time, some of the radioactive of aragonite crystals, the size and mineralogy — from left to right, optical interference seen uranium decays to lead, which shape of which are controlled by olivine, zircon and aragonite. under polarized light in the remains locked in the crystal. By the animal that forms the shell. Olivine — a magnesium–iron microscope. comparing the amount of uranium Aragonite is one of the calcium silicate• — was one of the first Zircon is especially robust remaining to the amount of new carbonate minerals often grown minerals to form in the solar and• is the oldest mineral found lead formed, zircon crystals can by organisms. Another is calcite, nebula, and is abundant in in Earth’s crust. It consists of be dated with great precision and which forms the hard parts of, Earth’s mantle and crust. This zirconium silicate, and typically accuracy, making zircon one of for instance, echinoderms, and photomicrograph shows olivine forms small, clear prisms such as the most valuable minerals for the shells of several types of crystals from the Allende these 0.1-millimetre-long crystals geochronology. plankton. These shells eventually meteorite; the crystals formed from Greenland. When zircons The mother-of-pearl lining become limestone — a type of during quenching of a millimetre- crystallize during the cooling of in• the shells of some molluscs rock that constitutes some 10% of sized droplet that originally circled granite magma, they incorporate — such as these virgin paua — is sedimentary deposits. M.T.R. review the extensive literature on the mineral- Earth-like planets. living and non-living world was set many years ogy of geological materials formed through On Earth itself, the emergence of life ago by N. L. Bowen in his book The Evolution Earth’s history. That history starts with cosmic gave rise to new opportunities in the min- of the Igneous Rocks3. dust and meteorites, and with the earliest rocks eral world. Living organisms can construct Hazen and colleagues2 provide an excellent that formed from magmas. Then came rocks chemical compounds that are not favoured by review of the mineral inventory of Earth and formed by metamorphic reactions in the heat thermodynamic equilibrium in the ambient the Solar System. In addition, they provide a of the deep crust, and rocks that formed at low environment and that would not have formed good sense of the evolution of the environments temperatures in Earth’s surface environments, spontaneously without the intervention of life. that permitted new minerals to form. How- and finally those minerals that are produced These compounds — for example aragonite in ever, their paper also includes a discussion on through the activities of living organisms. This some animal skeletons — provide advantages whether minerals can become extinct: they sug- analysis allows the division of Solar System his- for an organism that make it worthwhile to gest that, as planets evolve, some minerals that tory into three eras and ten ‘mineral evolution expend energy acquired from other life pro- were present in the early stages are succeeded stages’, each being characterized by the emer- cesses to synthesize them. The intervention by newer ones, never to recur on the scene, and gence of domains with new physico-chemical of life in Earth’s geochemical cycles therefore that this is akin to biological extinction. But the conditions that are expressed in the form of pro- greatly expanded the range of mineral species concept of mineral extinction is unsatisfactory gressively more diverse mineral assemblages. in Earth’s surface environments, and added because, unlike living species, mineral species All of the processes that combine the chemi- minerals such as the sulphate mineral gypsum do not depend on the transfer of information. cal elements into minerals are governed by a that we use in drywall panels and the haematite As a result, identical minerals will emerge on simple set of thermodynamic principles. used in red paint. This process coupled mineral the mineralogical scene repeatedly, as long as New minerals form if energy can be released evolution to biological evolution in that some the physical and chemical boundary conditions by recombination of their constituent ele- of the diversification of mineral species was can be re-established, so mineral species never ments from previous hosts. Minerals can only caused by diversification of biological species. become universally extinct. accommodate elements with specific chemi- It may seem problematic to use the concept Finally, the authors propose that the concept cal characteristics in their crystal lattices. The of evolution in connection with the non-living of mineral evolution should be used as a frame- chemical dissimilarity between the elements world of minerals. Hazen et al. discuss this issue work for teaching mineralogy rather than the becomes less pronounced with increasing at some length and show that it is semantically classic, crystallography-based system that temperature, so the early hot Earth had only a and etymologically permissible to use ‘evolu- currently forms the basis of most mineralogy few minerals such as olivine (Box 1), pyroxene tion’ to describe the change in any parameter as instruction. I find this suggestion undesirable: and feldspar. As the planet cooled, the elements a function of time. This may cause unnecessary the stringent systematic features of crystallog- found homes in more and more picky min- animosity towards the concept that they pro- raphy and mineral chemistry are characteris- eral structures, such as clay minerals and the pose, however, which could have been avoided tics of the physical world that help separate life zeolites we use in washing powder. As Hazen by using a more neutral term such as diversi- from its environment. et al. suggest, this cause of mineral species fication or differentiation. On the other hand, So I have reservations about some of the diversification must be a general feature of the scene for this type of analogy between the ideas associated with the principle of mineral 457 NEWS & VIEWS NATURE|Vol 456|27 November 2008 evolution. But otherwise I think it is an exciting DK 2100 Copenhagen, Denmark. concept that will do much to stimulate debate e-mail: [email protected] and enliven thinking in the usually staid field 1. Johnsen, O. Minerals of the World (princeton Univ. press, n of mineralogy. 2002). Minik T. Rosing is at the Nordic Center for 2. Hazen, R. M. et al. Am. Mineral. 93, 1693–1720 (2008). Earth Evolution, Natural History Museum 3. Bowen, N. l. The Evolution of the Igneous Rocks (princeton of Denmark, University of Copenhagen, Univ. press, 1928). 458.
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