Mineral evolution provides a new perspective on mineralogical science by including time as a factor in the consideration of the rapidly accumulating data on minerals, their composition, crystal structure, properties and occurrences on Earth and other planetary bodies. New modes of thinking are needed in order to arrange the data into coherent frameworks emphasizing changes in mineral diversity, composition and structural complexity with time. Approaching mineral diversity as a system amenable to quantitative treatment is one of the emerging fields in mineralogy, and has been attracting considerable interest and attention. A session on this theme was held at the Second European Mineralogical Conference in Rimini, Italy, September 11–15, 2016. Of the 26 presentations at the conference, seven were subsequently submitted as papers for inclusion in this special issue; we have added four not presented in this session, but included as very relevant to the theme of the special issue.

Christy reviews the traditional classification of chemical elements into “lithophile”, “chalcophile” and “siderophile” as first proposed by Goldschmidt and found it doesn't encompass all the nuances of chemical behavior, and thus proposes an empirical ten-step scale of geochemical preferences for these elements.

Grew et al. report lithian tourmaline and mica from a ca. 3000 Ma pegmatite, one of the two earliest known examples of the lithium-cesium-tantalum family of pegmatites in the geologic record. This pegmatite is most plausibly derived from a metasedimentary source by intrusion of hot mantle melts into the crust from below, thereby indicating the presence of “mature” continental crust atca.3000 Ma.

Vladimir Krivovichev et al. developed the concept of mineral systems, the set of chemical elements essential for the definition of a mineral species, that is, there are ten mineral systems with the number of essential components ranging from 1 to 10. This measure of chemical complexity increases from an average of 2.1–2.7 in minerals found in pre-solar nebulae and chondritic meteorites to 4.5 in post-Hadean minerals.

Sergey Krivovichev et al. present statistical analysis showing that strong and positive correlations exist between structural complexity and chemical complexity (in terms of the number of different chemical elements in a mineral) and that both have increased with the passage of geologic time, thus, as a first approximation, chemical differentiation is a major force driving the increase of complexity in minerals.

In two papers, Plášil applies the concept of structural complexity to the study of uranium minerals: uranyl-oxide hydroxyl-hydrate minerals (first paper,), and uranophane and uranophane-β (second paper ). He demonstrates that Shannon information provides a useful tool to investigate paragenetic sequences and the formation of metastable phases in uranium-based systems.

The paper byMajzlan et al. is a first systematic study of thermodynamic properties of the Fe(SO4)(OH)(H2O)x phases that may be useful for the physico-chemical modeling of acid mine drainage processes. These authors also note that structural complexity may play at least some role in the formation of this important group of minerals.

Pankova et al. report on the very complex crystal structure of ginorite and analyze dimensional reduction, chemical and structural complexities in the CaO–B2O3–H2O system.

Three other papers are focused on the concept of mineral diversity.Lykova et al.,demonstrate that there are several mineral varieties of the same mineral species, betalomonosovite, controlled by the mode of their formation and transformation. In contrast,Pekov et al.,provides in-depth analysis of paragenesis and diversity of fumarolic arsenates, using Tolbachik fumaroles as the most representative and chemically rich natural association of anhydrous arsenates.Chukanov et al. report new data on non-metamict ferriakasakaite-(La) and related minerals that increase the chemical diversity of minerals in the epidote supergroup.

SERGEY V. KRIVOVICHEV,  St Petersburg State University, Russia

EDWARD S. GREW, University of Maine, USA