silicify

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To convert into or impregnate with silica.
• intransitive verb To become converted into or impregnated with silica.

from The Century Dictionary.

• To convert into silica, as organic matter of any kind, especially wood.
• To become silica; be impregnated with silica.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb (Chem.) To convert into, or to impregnate with, silica, or with the compounds of silicon.
• intransitive verb To become converted into silica, or to be impregnated with silica.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb transitive to impregnate something with silica
• verb intransitive to be impregnated with, or converted into silica