The Relationship between Structural and Chemical Complexity of Boron Minerals with Geological Time
Edward S Grew, Univ Maine, Orono, ME, United States, Sergey V Krivovichev, St. Petersburg State University, Department of Crystallography, St. Petersburg, Russia and Robert M Hazen, Carnegie Inst, Washington, DC, United States
Contact First Author: Edward S Grew; esgrew@maine.edu
English Abstract:
Boron minerals are among the most structurally and chemically complex naturally occurring inorganic compounds. Of the 280 B minerals approved by the IMA, there are 250 species with known structures for which the age of the earliest reported occurrence in the geologic record has been reported. The earliest B minerals are 3550 Ma metamorphic tourmalines in the Isua supracrustal belt (Greenland), but many ephemeral species are restricted to Holocene deposits. We have analyzed structural complexity with the program package TOPOS using complexity parameters that provide Shannon information content per atom and per unit cell [Min. Mag. 77 (2013) 275-326]. The average contents per atom and per unit cell are 3.92 and 338 bits, respectively (compare 3.23 and 228 bits, respectively, for all minerals). Qingsongite, cubic BN (2 bits), is the simplest. There are 16 B minerals with information content per unit cell > 1000 bits. The structural complexity of rogermitchellite, Na6(Sr,Na)12Ba2Zr13Si39(B,Si)6O123(OH)12·9H2O (2321 bits) and byzantievite, Ba5(Ca,REE,Y)22(Ti,Nb)18(SiO4)4(PO4,SiO4)4(BO3)9O22[(OH),F]43·1.5H2O (1574 bits) results from chemical complexity based on the number of essential chemical constituents. However, chemically simpler hydrated Ca borates, e.g., ginorite, Ca2B14O20(OH)6·5H2O (1506 bits), ruitenbergite, Ca9B26O34(OH)24Cl4·13H2O (1492 bits), alfredstelznerite, Ca4B16O16(OH)24·19H2O (1359 bits), are also structurally complex, which we attribute to the interplay of borate polyanions and hydrogen bonding networks. The earliest complex borates are takéuchiite (1179 bits) and blatterite (1656 bits), which are reported uniquely from 1825 Ma deposits at Långban and Nordmark (Sweden). Plots of information contents per atom and per unit cell versus the earliest reported occurrences of B minerals in the geologic record reveal a broad increase in complexity, but this trend could result from preservation bias due to the ephemerality of many hydrated borates.
