June 2021 Archives

Vectors, Scalars, and How Science Works

The Oxford English Dictionary defines ‘vector’ as a quantity having direction as well as magnitude, and ‘scalar’ as a quantity having only magnitude, not direction. Much geological research starts with fieldwork, manifestly a vector activity. In Figure 1A, the geologists are exploring the intersection of a complex, 3-D body, the layered Klokken syenite, a 4 × 3 km igneous intrusion in the Gardar alkaline province of SW Greenland, with a mountainous 3-D land-surface. I described the unusual layering in Elements v10n1 (Parsons 2014). The igneous rocks were emplaced 1,166.3 ± 1.2 million years ago, and the 650 m of 3-D topography, which reveals the inner workings of the magma chamber, was carved by the advance and retreat of the mighty Greenland ice sheet in the last few thousand years. Only the age (a U–Pb age from baddelyite, ZrO2) is a scalar quantity.

Silicon Carbide Dust? The Answer is Blowin’ in the Wind

By Maitrayee Bose, Jack Schulte, Gregory Vance, Patrick Young and Sumner Starrfield |

Silicon carbide (SiC) minerals, which were argued to condense in stellar winds, were first isolated and imaged in 1987 (Bernatowicz et al. 1987). However, their existence in meteorites had been speculated from extensive noble gas studies. These studies suggested that SiC minerals are the carrier phases of the exotic 128,130Xe and 22Ne isotopic anomalies that can be found in primitive meteorites (e.g., Anders and Zinner 1993). In fact, SiC stardust does carry large isotopic anomalies, up to 4 orders of magnitude, both in light mass elements (e.g., carbon, nitrogen) and in medium mass elements (e.g., magnesium, iron, titanium). These anomalies can only be produced in stars through nuclear reactions occurring at extreme temperatures, by which the structure of the atomic nucleus is altered. The extreme isotopic anomalies in the SiC dust grains were not completely homogenized during the first 10 million years of planet formation and Solar System evolution, so they have kept their compositions intact until today. The dust grains carrying these enormous anomalies can be identified in extraterrestrial rocks that fall to Earth.

Exploring Earth and Planetary Materials with Neutrons

By Elements Magazine |

< Previous Issue June 2021 – Volume 17, Number 3 Next Issue > Download Table of Contents Digital Edition Download Issue Exploring Earth and Planetary Materials with Neutrons David R. Cole and Nancy L. Ross – Guest Editors Table of Contents EditorialFrom the EditorsTriple PointMeet the AuthorsMineral MattersThematic ArticlesSociety NewsBook ReviewCosmoElementsMeeting ReportCalendarParting Shots Overview Advertisers Next Issue…

Diversity among Editorial Boards of Elements and other selected Geochemistry, Cosmochemistry, Mineralogy and Petrology journals

By Olivier Pourret, Jennifer L. Middleton, Daniel E. Ibarra, Dasapta Erwin Irawan, Ashaki Rouff, Pallavi Anand, Aradhna Tripati, Amy J. V. Riches and Anthony Dosseto |

The publication of scientific work is foundational to our disciplines. To ensure equitable publication standards during the global flow of knowledge production, professional societies and publishers must take positive steps to avoid biases that might hinder the publication of scientific work (see Liévano-Latorre et al. 2020). Biases among editors and reviewers can be unconscious and be influenced by different aspects of an author’s identity: country of origin, first language, affiliation, gender identity, ethnicity, and/or other factors. These biases could result in challenges to publication rates and visibility in key journal forums for under-represented groups (Lerback et al. 2020). Ensuring that there is diversity in the peer review and publishing process, and on editorial boards, may help to eliminate bias.

v17n3 From the Editors

By John M. Eiler, Richard Harrison, Becky Lange and Jodi J. Rosso |

In just about every physical science course the concept of the atom is taught. Students are introduced to the three subatomic particles of electrons, protons, and neutrons. Usually, there is a lot of emphasis on electrons, because their configuration determines the chemical properties of an atom. And the protons get a lot of attention as well: who doesn’t like H+? Sadly, too often, neutrons are left in the “Oh, there is another part of an atom” category … that neutral subatomic particle that adds weight to the atom.

What Have Neutrons Ever Done for Us?

By Richard Harrison |

Upstairs in a secret and secure location,
mineralogical activists have gathered…

Imaging with Neutrons

By Gilberto Artioli and Daniel S. Hussey |

By exploiting the penetration, attenuation, and scattering properties of neutrons, images of matter in two or three dimensions reveal information unobtainable using other probes. Despite the limitation in brilliance of neutron sources, several neutron-based imaging techniques are essential to different aspects of modern geoscience. Typical examples include the evaluation of porosity in rocks and sediments, mapping of light elements in solids, noninvasive probing of cultural heritage objects, investigations of thick engineering components, and the exploration of diffusion and percolation processes of fluids within porous matrices, organo-inorganic composites, and living organisms. Techniques under development include simultaneous neutron and X-ray tomography in heterogeneous media, Bragg-edge imaging, and the possibility of porosimetry from dark-field imaging.

Probing Phase Transitions and Magnetism in Minerals with Neutrons

By Bryan C. Chakoumakos and John B. Parise |

The development of sophisticated sample environments to control temperature, pressure, and magnetic field has grown in parallel with neutron source and instrumentation development. High-pressure apparatus, with high- and low-temperature capability, novel designs for diamond cells, and large volume presses are matched with next-generation neutron sources and moderator designs to provide unprecedented neutron beam brightness. Recent developments in sample environments are expanding the pressure–temperature space accessible to neutron scattering experiments. Researchers are using new capabilities and an increased understanding of the fundamentals of structural and magnetic transitions to explore new territories, including hydrogenous minerals (e.g., ices and hydrates) and magnetic structural phase diagrams.

Probing the Structure of Melts, Glasses, and Amorphous Materials

By Chris J. Benmore and Martin C. Wilding |

Liquids, glasses, and amorphous materials are ubiquitous in the Earth sciences and are intrinsic to a plethora of geological processes, ranging from volcanic activity, deep Earth melting events, metasomatic processes, frictional melting (pseudotachylites), lighting strikes (fulgurites), impact melting (tektites), hydrothermal activity, aqueous solution geochemistry, and the formation of dense high-pressure structures. However, liquids and glassy materials lack the long-range order that characterizes crystalline materials, and studies of their structure require a different approach to that of conventional crystallography. The pair distribution function is the neutron diffraction technique used to characterize liquid and amorphous states. When combined with atomistic models, neutron diffraction techniques can determine the properties and behavior of disordered structures.

Nanoscale Structure and Dynamics in Geochemical Systems

By Andrew G. Stack, Hsiu-Wen Wang and David R. Cole |

Neutron scattering is a powerful tool to elucidate the structure and dynamics of systems that are important to geochemists, including ion association in complex aqueous solutions, solvent-exchange reactions at mineral–water interfaces, and reaction and transport of fluids in nanoporous materials. This article focusses on three techniques: neutron diffraction, which can reveal the atomic-level structure of aqueous solutions and solids; quasi-elastic neutron scattering, which measures the diffusional dynamics at mineral–water interfaces; and small-angle neutron scattering, which can show how properties of nanoporous systems change during gas, liquid, and solute imbibition and reaction. The usefulness and applicability of the experimental results are extended by rigorous comparison to computational simulations.