Subscripts and parentheses
A subscript counts atoms. CaF₂ means one calcium for every two fluorines — that's fluorite. Parentheses group an atom cluster that repeats as a unit. Cu₃(CO₃)₂(OH)₂ — azurite — has three coppers, two carbonate groups, and two hydroxyl groups. The parentheses tell you those groups stay bonded together throughout the structure.
The anion classification
Minerals are sorted scientifically by their dominant anion. Silicates (SiO₄ tetrahedra) make up 90% of crustal minerals. Carbonates (CO₃) include calcite, aragonite, dolomite, azurite, malachite. Sulfides (S) include galena, pyrite, sphalerite, stibnite. Oxides (O) include hematite, magnetite, cassiterite. Halides (Cl/F/Br) include halite and fluorite. Sulfates (SO₄), phosphates (PO₄), and tungstates (WO₄) round out the rest.
Reading complex formulas
Tourmaline's formula — (Na,Ca)(Mg,Li,Al,Fe)₃Al₆Si₆O₁₈(BO₃)₃(OH)₄ — looks brutal until you read it group by group. Comma-separated elements inside parentheses share a crystallographic site. Boron clusters as borate (BO₃) groups. Silicon clusters as a six-membered ring (Si₆O₁₈). Even the most fearsome formula is just a stack of structural ingredients.