At or near Earth's surface, sedimentary rocks form in two ways: by the accumulation of rock grains or by the formation of a solid from minerals dissolved in water. The fragments that go into making sedimentary rocks can be as big as boulders or as small as clay particles. Over long periods of time, the upper layers of debris compress the lower layers, squeezing out excess water or air trapped between the rock fragments. Under the pressure, individual fragments eventually dissolve and stick together, or the remaining fluid within the sediment brings in other substances that act as a cement, until the sediment has turned into rock. Scientists classify many sedimentary rocks based on the size of the particles that built the rock; mudstone and sandstone, for example, originally came from fine-grained mud and sand deposits that hardened over long time periods.

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.

When some minerals are ground into powders, they may be used as pigments, solid substances that change the color of the materials they are mixed with. The first pigments, known since prehistoric times, were iron oxides, which make warm, dark reds and browns. Other early pigments were made of lead, carbon (in charcoal form), malachite, and azurite. Today's paints may contain synthetic dyes in addition to natural pigments and fillers such as calcium carbonate, mica, silica, talc, and titanium dioxide. Minerals have been used as ingredients in facial makeup at least since the days of ancient Egypt, when women painted their eyes with kohl, a mixture containing finely ground galena, or lead sulfide. Modern-day cosmetics manufacturers avoid hazardous substances like lead and arsenic, but many of their products contain microscopic particles of minerals and their derivatives such as iron oxide (from goethite and other minerals), titanium dioxide (usually from ilmenite), talc, mica, and kaolinite.