The rock-forming silicates are the six groups of silicate minerals that make up most common igneous and metamorphic rocks: olivine, the pyroxenes, the amphiboles, the micas, the feldspars and quartz. The feldspars are of two kinds: potassium feldspar, such as orthoclase, and plagioclase, a series of feldspars containing sodium and calcium.
| group (example) | structure | formula | density |
| () | |||
| olivine | isolated tetrahedra | 3.32 | |
| pyroxene (augite) | single chains | 3.4 | |
| amphibole (hornblende) | double chains | 3.23 | |
| mica (biotite) | sheets | 3.09 | |
| mica (muscovite) | sheets | 2.82 | |
| potassium feldspar (orthoclase) | framework | 2.56 | |
| plagioclase (oligoclase) | framework | 2.65 | |
| quartz | framework | 2.62 |