P-207: An interlaboratory standard muscovite for argon and potassium analyses

Approximately 1100 grams of an 81-million-year-old muscovite, P-207, has been prepared as an interlaboratory standard for argon and potassium. The concentrate contains less than 1% of impurities. Twelve argon analyses made on two mass spectrometers and ten potassium analyses made by flame photometry give mean values of 1.253×10−9 mole Arrad40/g and 10.19% K2O for this standard. The M.I.T. standard biotite, B3203, the Switzerland standard muscovite, Bern 4M, and the U. S. Geological Survey standard granite, G-1, were analyzed to provide checks on procedure and calibration and to relate P-207 to these preexisting interlaboratory standards. The mean values obtained are: B3203, 1.733×10−8 mole Arrad40/g (four analyses), 8.95% K2O (two analyses): Bern 4M, 2.863×10−10 mole Arrad40/g (two analyses), 10.38% K2O (three analyses); G-1, 5.46% K2O (one analysis). Potassium-argon analyses of P-207 in twelve laboratories and rubidium-strontium analyses in three laboratories give the following results: ; ; Rb = 9.37 × 10−6 mole/g; Srrad87 = 3.17 × 10−9 mole/g; and common Sr = 0.113×10−6 mole/g.