Other forms of SiO2. a. Thick quartz overgrowth broken off of weathered grain in Decatur Bt. b. Unusual morphology for SiO2 from Consumo A sand. Aggregate on left, plant opal or crystobalite (more likely) on right. c. Unusual surface morphology on SiO2 grain. d. Unusual SiO2 morphology of 3-4 composite grains; Composite aggregate at upper right is mostly Si with small Al peak.
