Despite the abundance of silicons in the Earth's crust, not all minerals contain silicon. The atoms of many metals, which tend to lose electrons and become positively charged, like to bond with other atoms or groups of atoms that tend to gain atoms and become negatively charged. For example, atoms of sodium, a metal, and chlorine, a non-metal, pair up in equal numbers to form sodium chloride, also known as halite (or common table salt). Other important types of non-silicate minerals include carbonates, with metals bonded to groups of carbon and oxygen atoms; oxides, with metals joined to oxygen alone; sulfides, which consist of metal and sulfur atoms; and sulfates, in which groups of sulfur and oxygen atoms are joined with metal atoms.

One of the most striking, yet least diagnostic, features of many minerals is their color. Well-formed mineral crystals span the entire rainbow of tinctures, from red (cinnabar, garnet) to yellow (sulfur), green (malachite), blue (azurite, lazurite), and violet (the amethyst variety of quartz). Minerals containing iron and magnesium are often dark brown or dark green. Impurities, trace amounts of elements that do not normally belong in the mineral, may change the overall color of a crystal. For instance, depending on the trace amounts of impurities it contains, quartz may look colorless (no impurities), light pink (titanium, iron, or manganese), milky white (tiny bubbles of gas or liquid), purple (iron), yellow (iron), or brown (extra silicon). However, multiple minerals may have almost the same color, so scientists must rely on other physical properties to make definite identifications of mineral specimens.