touch·stone /ˈtʌʧˌston/
 試金石,標準


 Touch·stone n.
 1. Min. Lydian stone; basanite; -- so called because used to test the purity of gold and silver by the streak which is left upon the stone when it is rubbed by the metal. See Basanite.
 2. Fig.: Any test or criterion by which the qualities of a thing are tried.
    The foregoing doctrine affords us also a touchstone for the trial of spirits.   --South.
 Irish touchstone Min., basalt, the stone which composes the Giant's Causeway.

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 touchstone
      n : a basis for comparison; a reference point against which
          other things can be evaluated; "they set the measure for
          all subsequent work" [syn: standard, criterion, measure]