The Collaborative International Dictionary of English v.0.48:

Siliceous \Si*li"ceous\, a. [L. siliceus, fr. silex, silicis, a
   flint.]
   Of or pertaining to silica; containing silica, or partaking
   of its nature. [Written also silisious.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

siliceous
    adj 1: relating to or containing or resembling silica; "gritrock
           is siliceous sandstone" [syn: siliceous, silicious]