The Collaborative International Dictionary
Silicifying
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.
The specimens found . . . are completely silicified.
--Say.
Note: The silica may take the form of agate, chalcedony, flint, hornstone, or crystalline quartz.
Wiktionary
silicifying
vb. (present participle of silicify English)