The Collaborative International Dictionary of English v.0.48:

Silicify \Si*lic"i*fy\, v. i.
   To become converted into silica, or to be impregnated with
   silica.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Silicify \Si*lic"i*fy\, v. t. [imp. & p. p. Silicified; p. pr.
   & vb. n. Silicifying.] [L. silex, silicis, a flint + -fy:
   cf. F. silicifier.] (Chem.)
   To convert into, or to impregnate with, silica, or with the
   compounds of silicon.
   [1913 Webster]

         The specimens found . . . are completely silicified.
                                                  --Say.
   [1913 Webster]

   Note: The silica may take the form of agate, chalcedony,
         flint, hornstone, or crystalline quartz.
         [1913 Webster]