text: In the 1930s, USSR geochemist Alexander Fersman defined the relative abundance of chemical elements in geological objects, denoted in percents, as . This was in honor to the American geochemist Frank Wigglesworth Clarke, who pioneered in estimating the chemical composition of Earths crust, based on Clarke and colleagues extensive chemical analysis of numerous rock samples, throughout 1889 to 1924().
  Examples based on Fersman's definition:
  * : When the whole mass of a planet X is  , and the mass of oxygen there is  , then the weight clarke of oxygen in planet X is  (dimensionless)
  * : When the whole count of atoms in a rock Y is  , and the atom count of silicon there is  , then silicon's clarke of atom count in rock Y is  (dimensionless)
  * Fersmans "clarke of Earths crust" is the Earth's surface including 16 km-thick lithosphere, hydrosphere and atmosphere.