ABSTRACT
The term silica refers to silicon dioxide (SiO2), in its various forms, and silica minerals are the second most abundant group, behind silicate minerals discussed in Chapter 8 (Monger and Kelly 2002). The silica minerals include quartz (in several crystalline forms) and opals. All of them are tectosilicates, formed from strongly bound SiO4 tetrahedra, which were discussed in Section 8.1.
