Causes of anomalous mineralogical diversity in the Periodic Table

Abstract

When crustal abundance (A, measured in atomic parts per million) of a chemical element is plotted vs. number of mineral species in which that element is an essential constituent (S), a significantly positive correlation is obtained, but with considerable scatter. Repeated exclusion of outliers at the 90% confidence level and re-fitting leads, after the sixth iteration, to a steady state in which 40 of the 70 elements initially considered define a trend with log S = 1.828 + 0.255 log a (r = 0.96), significantly steeper than the original. Three other methods for reducing the effect of outliers independently reproduce this steeper trend. The 'diversity index' D of an element is defined as the ratio of observed mineral species to those predicted from this trend. D separates elements into three groups. More than half of the elements (40 of 70) have D = 0.5–2.0. Apart from these 'typical' elements, a group of 15 elements (Sc, Cr, Ga, Br, Rb, In, Cs, La, Nd, Sm, Gd, Yb, Hf, Re and Th) form few species of their own due to being dispersed as minor solid solution constituents, and a hitherto unrecognized group of 15 elements are essential components in unusually large numbers of minerals. The anomalously diverse group consists of H, S, Cu, As, Se, Pd, Ag, Sb, Te, Pt, Au, Hg, Pb, Bi and U, with Te and Bi by far the most mineralogically diverse elements (D = 22 and 19, respectively). Possible causes and inhibitors of diversity are discussed, with reference to atomic size, electronegativity and Pearson softness, and particularly outer electronic configurations that result in distinctive stereochemistry. The principal factors encouraging mineral diversity are: (1) Particular outer electronic configurations that lead to a preference for unique coordination geometries, enhancing an element's ability to form distinctive chemical compounds and decreasing its ability to participate in solid solutions. This is particularly noteworthy for elements possessing geometrically flexible 'lone-pair cations' with an s2 outer electronic configuration. (2) Siderophilic or chalcophilic geochemical behaviour and intermediate electronegativity, allowing elements to form minerals that are not oxycompounds or halides. (3) Access to a wide range of oxidation states. The most diverse elements can occur as anions, native elements and in more than one cationic valence state.

Advances and Opportunities in Ore Mineralogy

“…In fact, if we include samples from abandoned mines and oxidised ores at the surface associated with historical mine workings, mineral deposits account for roughly half of the new minerals that were accepted between 2011 and 2016. This is perhaps unsurprising as mineral deposits are anomalous in elements that are prone to greater mineralogical diversity [181], and even more importantly, will contain various combinations of those elements. Sulphosalts represent a particularly fertile area of ore mineral research, with more than a dozen new sulphosalt species being approved since the publication of the report of the IMA Commission on Ore Mineralogy Sub-Committee on Sulphosalts [182].…”

“…In fact, if we include samples from abandoned mines and oxidised ores at the surface associated with historical mine workings, mineral deposits account for roughly half of the new minerals that were accepted between 2011 and 2016. This is perhaps unsurprising as mineral deposits are anomalous in elements that are prone to greater mineralogical diversity [181], and even more importantly, will contain various combinations of those elements.…”

The Thermodynamics of Selenium Minerals in Near-Surface Environments

“…As shown [9,10], any mineral can be assigned to a specific system, each component of which is a species-defining chemical element (cf. [11][12][13]) determined by the rules of the new mineral species definition [14][15][16]. For mineral coding, we used the sequence of speciesdefining chemical element symbols according to the so-called "thermochemical" sequence of chemical elements (Figure 1) [9,10].…”

210Pb and 210Po in Geological and Related Anthropogenic Materials: Implications for Their Mineralogical Distribution in Base Metal Ores

“…No less than 262 different uranium minerals are currently recognised, one of the largest numbers for any element in the periodic table [190]. Uranium thus belongs among a small group of elements whose mineralogical diversity is anomalous compared to its low crustal abundance.…”