February 2009 - Scientific Exploration of the Moon
Our current understanding of the Moon’s history, interior structure, and chemical composition is based in large part on geochemical data acquired from samples from the U.S. Apollo and Soviet Luna missions; data acquired by Apollo geophysical instruments; orbital geochemical and spectral data acquired by robotic missions from the U.S., Japan, and China; analysis of lunar meteorites derived from previously unsampled regions of the Moon; and Earth-based radar observations and infrared spectral reflectance data. All of these efforts have contributed to a preliminary understanding of the origin of the Moon and the processes that have affected its surface and interior. Isotopic analyses of impact-generated samples have placed constraints on the time-dependent meteorite flux that not only affected the Moon but also the Earth and other objects in the inner solar system. In this issue of Elements, leading scientists discuss the major concepts that underpin our current understanding of the Moon, as well as scientific plans for international scientific exploration by robotic and human missions.
Of all naturally occurring clays, bentonites are arguably the most interesting, versatile and useful. This issue of Elements describes how these fascinating materials occur and how they are used in all manner of applications. Composed predominantly of swelling minerals (smectites) and formed mainly from the alteration of volcanoclastic rocks, bentonites are used by geologists for stratigraphic correlation. Bentonite deposits are mined worldwide as they are commercially very valuable. Because of their physicochemical properties, bentonites are used in a wide variety of industrial applications, including the drilling industry, foundries, civil engineering, adsorbents, filtering, etc. Recent formulations of polymer–smectite nanocomposites have been used in industry to make new materials with amazing properties and diverse applications. Bentonites play an important role in the protection of the environment from industrial waste and pollutants and have also been used in medical applications in human health.
Most gems are natural minerals, which, although scarce and small, have a major impact on society. Their value is directly related to proper identification. The determination of the species is key, of course, and must be done non-destructively. This is where classical tools of mineralogy come into play. However, other issues are paramount: Has this gem been treated? Is it natural or was it grown in a laboratory? For certain varieties, being able to tell the geographical provenance may enhance value considerably. These issues necessitate cross-linking the formation of gems with their trace-element chemistry. These unusual mineralogical and geochemical challenges make the specificity of gemology, a new and growing science, one of the possible futures of mineralogy.
August 2009 - Mineral Magnetism: From Microbes to Meteorites
Magnetic minerals are ubiquitous in the natural environment. They are also present in a wide range of biological organisms, from bacteria to human beings. These minerals carry a wealth of information encoded in their magnetic properties. Mineral magnetism decodes this information and applies it to an ever increasing range of geoscience problems, from the origin of magnetic anomalies on Mars to quantifying variations in Earth’s paleoclimate. The last ten years have seen a striking improvement in our ability to detect and image, with higher and higher resolution, the magnetization of minerals in geological and biological samples. This issue is devoted to some of the most exciting recent developments in mineral magnetism and their applications to Earth and environmental sciences, astrophysics, and biology.
Gold fascinates researchers in many sciences. As well as being attractive as a precious metal, gold has important physical and electrical properties that cause it to be an ’advanced material’ for manufacturing and drug delivery in medical science. Geologically, gold can be transported in solution in ambient- as well as high-temperature fluids, and its mineralogy, composition and crystallography are often used to decipher and interpret the genesis of different gold-bearing ore systems. Because gold is a metal, its study requires a detailed understanding of metallography. Finally, nanocrystals of gold and its alloys display unique properties, and these products are finding widespread application in manufacturing and are also seen in the natural environment. This issue of Elements describes new observations about a metal that has fascinated humans since early times. Current research spans the fields of geochemistry, crystallography, and metallurgy, and includes novel studies in the materials sciences.
December 2009 - Metal Stable Isotopes: Signals in the Environment
During the past decade it has been recognized that the stable isotope compositions of several metallic elements vary significantly in nature due to both biotic and abiotic processing. While this leap in our understanding has been fueled by recent advances in instrumentation and techniques in both thermal ionization and inductively coupled plasma mass spectrometry, the field of metal stable isotope geochemistry has finally moved beyond a focus on development of analytical techniques and toward using the isotopes as source and process tracers in natural and experimental systems. Often termed the “non-traditional stable isotopes,” metal stable isotope systems have found wide application in the geological, hydrological, and environmental research realms and are enjoying a rapidly expanding presence in the scientific literature. This issue of Elements will focus on several intriguing aspects of low-temperature metal stable isotope geochemistry.