silica
sil.i.ca \'sil-i-k*\ n [NL, fr. L silic-, silex flint, quartz] : silicon dioxide SiO2 occurring in crystalline, amorphous, and impu re forms (as in quartz, opal, and sand respectively)
Webster's English Dictionary Webster's English Dictionarysil.i.ca \'sil-i-k*\ n [NL, fr. L silic-, silex flint, quartz] : silicon dioxide SiO2 occurring in crystalline, amorphous, and impu re forms (as in quartz, opal, and sand respectively)