Within a short period of one year (November 1992‐ October 1993), ninety‐two IWG‐Member laboratories have been able to characterize the chemical composition of a candidate reference sample, Zinnwaldite ZW‐C, a Li‐mica, reputed difficult to analyse because of its high contents of F and rare alkali elements and of the presence of refractory minerals. Thanks to the help of 163 analysts from the 92 laboratories, it has been possible to assign working values for 20 major and minor elements including the rare alkali elements and for 43 trace elements; all the working values receive the status of recommended values, except H20, C02, LOI, CI and S. It is, indeed, a rare success for such a difficult sample!

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