EVOLUTION OF THE MINERALS OF BERYLLIUM, A QUINTESSENTIAL CRUSTAL ELEMENT

Some 106 minerals containing essential beryllium have been approved as valid species; these include 64 silicates, 28 phosphates and arsenates, 9 oxides and hydroxides, 4 borates and one carbonate. Beryllium minerals are found most abundantly and in greatest diversity in granitic pegmatites, alkaline and peralkaline pegmatites, hydrothermal deposits associated with volcanic and shallow-level plutonic rocks, and skarns, whereas non-metasomatic metamorphic occurrences are minor and sedimentary occurrences unknown except for placers. Beryllium is a rare element, and therefore minerals containing essential Be appear only after extensive differentiation, which explains the relatively late first appearance of Be minerals in the geologic record. Based on reported finds, the oldest Be minerals are Mesoarchean, when four species formed in granitic pegmatites associated with greenstone belts (~2860 Ma, Pilbara Craton, Australia). Eight more species are found in Neoarchean granitic pegmatites and granulite-facies rocks (Yilgarn Craton, Australia; Bird River Province, Canada). Anatectic pegmatites in the ultrahigh-temperature Napier complex (Antarctica) introduce three more species in the earliest Paleoproterozoic, the last to appear before a burst of 26 new species at the close of the Paleoproterozoic (~1800-1715 Ma) in both pegmatites (e.g., Norrö, Sweden; Tysfjord, Norway, Tiptop, SD, Red Ace, WI) and complex skarn deposits of the Långban type in Sweden. From about 1700 Ma to 1 Ma, the number of new Be minerals increased relatively steadily, with a surge of 13 new species at 1160 Ma (Ilímaussaq peralkaline complex, Greenland). The youngest species is no more than 1 Ma in age; it was discovered in the Eifel volcanics, Germany. All of the “principal” episodes of Be mineralization cited by Barton & Young (2002, Rev. Mineral. Geochem., v. 50, p. 654) occurred after 1600 Ma. Barton & Young cautioned that most Be deposits are concentrated at shallow levels in the Earth’s crust, and thus older occurrences could have been lost to erosion. Alternatively, the increasing diversity of Be minerals could have resulted from the increasing diversity and mixing of geologic materials as the Earth’s crust is recycled by tectonic processes.