Scientific and technological innovation from mineral geonomics - a dual source microfocus single-crystal diffractometer for UK geoscience

Minerals are critically involved in all global processes, including deep earth tectonics and geohazards, dynamic environmental changes at the Earth's surface, and forming the fundamental skeletal structures of many of Earth's organisms. Since the early 20th century, crystallographers have studied and classified the crystal structures of minerals and used this information to further our understanding of geodiversity, the geological evolution of Earth and the exploitation of minerals as critical resources for developing societies. However, as our knowledge of the mineral kingdom developed and society's understanding of the global human impact has improved, so the need to study more complex and challenging materials has become increasingly urgent. Unfortunately, such minerals from unique natural environments including, diverse biogeochemical systems, legacy mining / industrial sites, modern waste management and recycling systems, fossils, plants and animals, and extremes of temperatures, pressure and stresses, have to-date proven too challenging to be structurally characterised at the atomic scale.

The main properties that make them so challenging to study include their extremely small size, chemical complexity and heavy atom/light atom combinations, huge topological units (large repeating patterns), or limited stability/crystallinity. These previously insurmountable technical challenges can now be addressed, due to major advances in hardware and software relating to X-ray crystallography methods in the past 5 years that now allow innovative structural science on these minerals linking nano-scale phenomena with large-scale geological processes - a fundamental goal of geoscience. The instrument proposed here is a unique single-crystal X-ray diffractometer equipped dual Ag/Mo (silver and molybdenum) high-flux X-ray micro-source and Cd-Te (cadmium-tellurium) area detector.

The dual source allows us to change the X-ray wavelength to optimise the experiment, for example when using high pressure equipment (known as diamond anvil cells, DAC) much of the diffraction data are shielded by the DACs when using a Mo X-ray source. This problem is alleviated by using an Ag X-ray source and consequently a more complete data set with high numbers of diffraction peaks can be collected. Traditional silicon detectors are reasonably efficient for Mo X-rays, but their efficiency plummets when using shorter wavelength X-rays such as from an Ag X-ray source. Newly developed Cd-Te detectors maintain their efficiency at long and short wavelengths allowing us to conveniently change X-ray source without any loss in counting statistics. Finally, microfocus X-ray sources have a much higher flux and longer lifespan when compared to traditional X-ray sources.

This new diffractometer will expand our knowledge of mineral geodiversity, enhancing national and international collections and databases. We will be able to study minerals from the Earth's deep interior under realistic pressure and temperature conditions or as tiny inclusions from mantle diamonds, allowing us to refine our models of Earths structure, composition and dynamics. Furthermore, understanding the fundamental atomic scale structures of challenging minerals provides critical data for models of metal cycling, ore-forming systems, nutrient transport and toxicity/remediation. Such information is held within microscale neo-forming phases at the mineral:water interface, often mediated by microbial communities utilising minerals for energy whilst co-precipitating new phases. Solving the structures of minerals with technological potential or minerals hosting technology enabling elements will enhance the link between geometallurgy, mineral engineering and functional materials driving the technological exploitation of minerals utilising sustainable, low energy, low waste technology.