Some chemical compounds, such as ordinary salt (also known as sodium chloride), dissolve easily in water. When these dissolved compounds exceed their maximum possible concentration in a body of water, they begin to form crystalline solids and precipitate out of solution. Also, when an enclosed body of water - one that can no longer drain to the ocean - dries up, it leaves behind layers of solid materials that did not evaporate. In both cases, the resulting layers of sediments eventually form rocks. Halite (another word for table salt or sodium chloride) is the most common component of these sedimentary rocks, which may also contain gypsum and anhydrite (two forms of calcium sulfate), sylvite (potassium chloride), and calcite (calcium carbonate). The Bonneville Salt Flats in northern Utah are the sedimentary remnants of a huge prehistoric inland sea that extended far beyond the present-day Great Salt Lake.

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.