Impact processes are central to the formation and evolution of the Solar System and the modification of planetary surfaces. On Earth, asteroid impacts played a critical role during Earth history; they delivered the constituents of our planet, were responsible for the formation of major ore deposits, and affected life on Earth. Studying impacts and their effects is a very active field at the crossroads of many scientific disciplines, from mineralogy to environmental science. This issue will focus on the mineralogical, geochemical, and petrological aspects of terrestrial impact structures, and in particular on the latest developments in the relevant fields.
Studies of mineral–microbe interactions lie at the heart of the emerging field of geomicrobiology, because minerals are the fundamental Earth materials with which microbes interact. Microbes are found in a number of the Earth’s extreme environments and also in extraterrestrial materials. In spite of the diverse geological environments in which microbes are found and the various approaches taken to study them, a common thread—mineral–microbe interactions—connects all these environments and experimental approaches and places them under the same umbrella: geomicrobiology. Minerals provide microbes with energy and living habitats, and microbes impact mineral weathering and diagenesis. The recognition of mineral–microbe interactions has revived the classical discipline of mineralogy, and microbes discovered in various habitats have provided microbiologists with unique opportunities for study. This issue considers microbially mediated mineral dissolution, precipitation, and transformation, and the synergistic relation between minerals and microbes for energy acquisition. These interactions have important implications for contaminant remediation.
On March 11, 2011, an earthquake and tsunami hit Japan, killing more than 20,000 persons, displacing tens of thousands, and causing havoc in the infrastructure and economy of the country. In the aftermath of this tragedy, the cooling systems of three of the operating reactors at the Fukushima Dai-ichi nuclear power station failed and meltdown of the reactor cores occurred. Over the following days, a series of hydrogen gas explosions took place. Radionuclides (mainly 131I and 137Cs) were released to the atmosphere and transported over many tens of kilometers from the site, contaminating soil and water. Seawater was used to cool the damaged reactor cores, and water contaminated with radioactivity was released to the ocean. Considerable amounts of used fuel were stored in nearby pools, and with the loss of water, the pools contributed to the release of radioactivity. One year after the tragedy at Fukushima, this issue of Elements provides a summary of what is known about the environmental impact of this nuclear accident.
Nothing that geoscientists learn as students prepares them for interpreting rock textures as complex as those found in pegmatites. Understanding the textures and mineral zonation of granitic pegmatites is tantamount to understanding the fundamental process of crystallization. It is a challenge to our ability to discern, beyond reasonable doubt, what is igneous and what is hydrothermal. This is the context that has drawn many professional geoscientists to the study of pegmatites for all or part of their careers. In addition, granitic pegmatites are important to our society as sources of raw materials for glasses and ceramics, silicon for microprocessors, and specialty metals including Li, Cs, Be, Nb, Ta, Sn, REE, and U. A very few pegmatites provide some of the most highly prized mineral specimens and colored gems found in national museums and personal collections around the world. No other rock type presents such a diversity of economic commodities in such concentrated fashion.
Rare earth–based materials have practical applications in transportation, renewable energy, medicine, household items, visual arts, forensic science, and defense, and thus are essential to the progress of humankind. The rapid development and implementation of innovative and green technologies in the past decade have resulted in greatly increased demand for rare earth elements (REE). This demand has been amplified by the current situation in the supply market and by growing public concern about unlawful or unethical extraction of certain rare-metal resources. The renewed interest in rare earth resources in the exploration and public sectors requires a much better understanding of these resources and their host rocks than currently available. This thematic issue will present a comprehensive overview of the key geological, geochemical, and mineralogical aspects of REE distribution in the crust and principal deposit types. It will also discuss economic, political, and environmental issues related to REE mining.
By 2030, about 60% of the human population will live in cities. Clearly, anthropogenic activities in urban environments affect geochemical cycles, water resources, and the health of ecosystems and humans globally. Past practices are still having biogeochemical impacts today, and in many cases remediation is needed. Both natural and man-made disasters greatly change the geochemistry of urban areas. Understanding past impacts can aid in future disaster planning. An increased awareness of the geochemical and mineralogical effects of urbanization on geochemical cycling will aid urban planners in the effort to make urban development sustainable.