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WikiProject Moon (Rated Start-class, High-importance)
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obscure symbols[edit]

Please, explain for me "Canonical composition of KREEP includes 1% (wt) of potasium and phosphorus oxides, 20-25 ppm of Rb". what do "ppm" and "Rb" refers to in this sentence? --aad_Dira (talk) 10:48, 1 February 2011 (UTC).