The structural classes
Nesosilicates — isolated tetrahedra (olivine, garnet, zircon, kyanite). Sorosilicates — two tetrahedra sharing one oxygen (epidote, hemimorphite). Cyclosilicates — rings (tourmaline, beryl, cordierite). Inosilicates — single chains (pyroxenes) or double chains (amphiboles). Phyllosilicates — sheets (micas, talc, clays, kaolinite). Tectosilicates — three-dimensional frameworks (quartz, feldspar, zeolites, the most common rock-forming minerals).
Why this matters for collectors
Each structural class has characteristic habits, cleavages, and optical properties. Phyllosilicates always cleave in one direction (the sheet) — micas peel into perfect basal plates. Inosilicate amphiboles cleave parallel to the chains, giving classic 56°/124° angles between cleavage faces. Tectosilicate quartz has no cleavage at all because the framework is fully interconnected.
Common collector species
Garnet (nesosilicate). Zircon (nesosilicate). Tourmaline (cyclosilicate). Beryl — emerald, aquamarine, morganite (cyclosilicate). Pyroxene group — augite, diopside, spodumene (inosilicate). Amphibole group — hornblende, tremolite (inosilicate). Mica group — biotite, muscovite, lepidolite (phyllosilicate). Quartz — all varieties (tectosilicate). Feldspar group — orthoclase, plagioclase (tectosilicate).