[Rockhounds] concrete/cement

[June Young]

I have a piece of jasper  that appears to have concrete/cement on it.  I have picked off a great deal of the concrete but it still has a white colored coating.  Will muratic acid take off this final layer?  If so, should it go in at 100%?  How long should it stay in?  Will it need to be scrubbed with a steel brush?  Does muratic acid loose its effectiveness if it has been around for many years?
  Thanks for your help.
  June

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