A uranium-containing mineral known as ewingite, originally found in a damp mine wall in the Czech Republic, has been shown to have a structure with a complexity almost twice that of any previously known mineral. The mineral and its structure were reported by scientists in the USA [T A Olds et al Geol; DOI: 10.1130/G39433.1]
The complexity of a mineral is measured in terms of bits per unit cell. Many common minerals crystallize with a complexity measure of just over 200. Mineralogists and crystallographers will perceive a complex mineral has having a measure of around 1000 bits per unit cell, although only about 2.5% of known minerals fall into this category. According to Peter Burns of the University of Notre Dame, in Indian, and colleagues the recently discovered ewingite somehow crams almost 13000 bits into its unit cell with its formula - Mg8Ca8(UO2)24(CO3)30O4(OH)12.138H2O - perhaps hinting at its complexity.
"Minerals at 1,000 bits are considered very complex, but only about 2.5 percent of known minerals receive that designation," confirms Burns. "In comparison, ewingite measures at 12,684.86 bits per unit cell, essentially doubling the measuring stick that mineralogists currently use." The team is currently attempting to synthesize the mineral in the laboratory so that they can better understand the conditions that led to its formation. "The structure of ewingite contains nanometer-scale anionic uranyl carbonate cages that contain 24 uranyl polyhedra, as well as calcium and magnesium cations and water groups located in interstitial regions inside and between the cages," the team reports. "The discovery of ewingite suggests that nanoscale uranyl carbonate cages could be aqueous species in some systems, and these may affect the geochemical behavior of uranium," they add.
Burns muses on the fact that this mineral may well have not existed until people opened up the mine in which it was discovered and allowed the particular temperature, pressure, humidity, and atmospheric conditions to interact with other materials locked in the earth until that time. The researchers are working with the Carnegie Institute to gather existing data on uranium-based minerals. They hope to spot variations in the information we already have about such minerals to determine whether their formation has also arisen through human activities, such as mining.
Ewingite was named after Rodney C. Ewing, who is Frank Stanton Professor in Nuclear Security at Stanford University. The name recognizes his contributions to the fields of mineralogy and nuclear science. The mineral was discovered in the Plavno mine in the Jáchymov ore district, western Bohemia, Czech Republic. An intriguing aside is that this mine is in the same region that provided experimental materials for Marie Curie's pioneering scientific work in the early twentieth century that led to the discovery of what we now know as the elements polonium and radium.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".