In the 1930s, USSR geochemist Alexander Fersman defined the relative abundance of chemical elements in geological objects, denoted in percents, as Russian: кларки, lit.
[F 1]: 141 This was in honor to the American geochemist Frank Wigglesworth Clarke, who pioneered in estimating the chemical composition of Earth's crust, based on Clarke and colleague's extensive chemical analysis of numerous rock samples, throughout 1889 to 1924([C 1][C 2][C 3][C 4][C 5][C 6][C 7][C 8][C 9]).
Examples based on Fersman's definition: Russian: кларки is synonymous to "the relative abundance of elements" in any object, either in weight ratio or in atomic (number of atoms) ratio, regardless of how "Earth's crust" is defined, and denotation is not restricted to percents.
[x 1] In the English speaking world, the term "clarke" was not even used in Wells(1937)[U 1]: 4 which introduced Fersman's proposal, nor in later USGS articles such as Fleischer(1953).
Several of the following constraints may apply: Another peculiarity in Japan is the existence of a popular version of data, which was tabulated in reference books such as the annual "Chronological Scientific Tables" (RCST1939(1938)[R 1]: E46 ), the "Dictionary of Physics and Chemistry" (IDPC(1939)[I 1]: app.VI ) and other prominent books on geochemistry and chemistry.
As geological definition of "Earth's crust" evolved, the "10 mile-deep" approximation were deemed out-of-date, and some people considered the term "clarke number" obsolete too.
[H 2] Yet other people may have meant broader senses, not limiting to Earth's crust, leading to confusion.
Despite being removed from major reference books, data from Kimura(1938) and phrases such as "the Clarke number of iron is 4.70", unsourced, continue to circulate, even in the 2010s (example:[x 7]: 799 ).
Technical definition of "clarke", "Earth's crust" and "lithosphere" differ among authors, and the actual numbers vary accordingly, sometimes by several times.
Tables of historical data for some elements of their relative abundance in Earth's crust.