Structural and chemical complexity of minerals: an update

Abstract

The complexities of chemical composition and crystal structure are fundamental characteristics of minerals that have high relevance to the understanding of their stability, occurrence and evolution. This review summarises recent developments in the field of mineral complexity and outlines possible directions for its future elaboration. The database of structural and chemical complexity parameters of minerals is updated by H-correction of structures with unknown H positions and the inclusion of new data. The revised average complexity values (arithmetic means) for all minerals are 3.54(2) bits/atom and 345(10) bits/cell (based upon 4443 structure reports). The distributions of atomic information amounts, chemIG and strIG, versus the number of mineral species fit the normal modes, whereas the distributions of total complexities, chemIG,total and strIG,total, along with numbers of atoms per formula and per unit cell are log normal. The three most complex mineral species known today are ewingite, morrisonite and ilmajokite, all either discovered or structurally characterised within the last five years. The most important complexity-generating mechanisms in minerals are: (1) the presence of isolated large clusters; (2) the presence of large clusters linked together to form three-dimensional frameworks; (3) formation of complex three-dimensional modular frameworks; (4) formation of complex modular layers; (5) high hydration state in salts with complex heteropolyhedral units; and (6) formation of ordered superstructures of relatively simple structure types. The relations between symmetry and complexity are considered. The analysis of temporal dynamics of mineralogical discoveries since 1875 with the step of 25 years show the increasing chemical and structural complexities of human knowledge of the mineral kingdom in the history of mineralogy. In the Earth's history, both diversity and complexity of minerals experience dramatic increases associated with the formation of Earth's continental crust, initiation of plate tectonics and the Great Oxidation event.

Evolution of symmetry index in minerals

“…This feature can also be seen in 14, which shows an almost reverse dependency of symmetry index on the number of unique elements in a mineral with minerals having between four and eight different essential elements having the lowest symmetry index. (Krivovichev et al, 2022) discusses the similar, lognormal distribution of the number of atoms per formula or per unit‐cell as a result of balance between the need to accommodate different elements in the same cell and the tendency of crystal structures to be as simple as possible.…”

Wodegongjieite, ideally KCa3(Al7Si9)O32, a new sheet silicate isostructural with the feldspar polymorph kokchetavite, KAlSi3O8

“…Complexity is best expressed in terms of the Shannon information concept (e.g. Krivovichev, 2012, 2013, 2020; Krivovichev et al , 2022; Zolotarev et al , 2019). Shannon information in bits reflects diversity of structural sites (information per atom) and both diversity of sites and the number of atoms in the unit cell (information per cell).…”

Bobtraillite from Gejiu hyperagpaitic nepheline syenite, southwestern China: new occurrence and crystal structure

“…Only two boroncontaining zirconium silicates have been found in nature so far: bobtraillite and rogermitchellite. According to the total structural information content, they are both classified into complex mineral structure (> 1000 bits per unit cell) (Grew et al, 2016); especially, rogermitchellite has the most complex crystal structure of all the boron minerals with I G, total = 3019 bits and is the 20th most complex of the 4443 structures reported to data (Krivovichev, 2013;Krivovichev et al, 2022). The two chemically and structurally related minerals are both found in hyperagpaitic nepheline syenites at Mont Saint-Hilaire, Quebec, Canada.…”